Mac

Since Apple first made major macOS upgrades available in downloadable form rather than offering DVDs (remember those?), downloading an installer meant just that: you got a separate installer app on your disk that you could open by double-clicking it. In contrast, minor updates were available through Software Update, requiring only a couple of clicks to install.

For the past several years, however, Apple has offered even major upgrades—like going from macOS 26 Tahoe to macOS 27 Golden Gate—via Software Update (that is, System Preferences > Software Update in Monterey or earlier, or System Settings > General > Software Update in Ventura or later). Besides requiring fewer steps, the downloads available through Software Update tend to be smaller and thus quicker to download than full installers.

If your Mac supports macOS 27 Golden Gate and it hasn’t yet been installed, a little badge appears on the System Settings icon and you may be tempted to simply click Upgrade Now and step through the update process there. The badge names whatever the current version of macOS 27 is, rather than 27.0.0).

Although you can use this approach, I recommend against it, for the following reasons:

• The downloads may be smaller, but you don’t get a standalone installer. That means you can’t copy it to another Mac or make a backup of the installer in case you need to use it again (see how to keep a copy).
• As a consequence of not having a full installer app, you can’t make a bootable installer (see making a bootable installer).
• The installer you get via Software Update does not prompt you to choose a destination (see selecting a destination); it can be used only for updating the copy of macOS on your current startup volume. That also means this approach can’t be used with Plan B. So, if you try using Software Update with Plan A and you have a problem, you’ll have to download the full installer anyway to switch to Plan B.

If you do choose to go the Software Update route, most of the installation process will be the same, and you’ll follow the same steps afterward.

Make final preparations

Now that you know which basic installation technique you’re going to use, you’re nearly ready to proceed. Your next major step (which could take hours, or even longer) is to obtain the macOS 27 installer; then I’ll recommend a few other quick, last-minute tasks before you dive in.

Obtain the installer

Depending on your situation, obtaining the macOS 27 installer may be a trivial matter of a few clicks, or it may be an involved ordeal.

If you are comfortable with the trade-offs above, you don’t have to perform a separate download at all; simply go to System Settings > General > Software Update, or System Preferences > Software Update in Monterey or earlier, and click Upgrade Now. Then click Continue, agree to the software license if prompted to do so, and skip ahead to the installation itself.

If you don’t pursue this path, you must go through a few non-obvious steps to download the macOS 27 installer, which, like Tahoe, is not available from the Mac App Store.

The easiest way to proceed is to obtain a direct download link that points directly to Apple’s servers. I can’t overemphasize how important it is to download directly from Apple. Apple doesn’t publicize such links, but the site Mr. Macintosh has very helpfully collected them for us. The site Mr. Macintosh collects them; every link there points to swcdn.apple.com, a legitimate Apple download server.

On that page, look for the most recent entry in the PUBLIC Full Installer table. Click the link to download InstallAssistant.pkg.

You might be thinking, “Don’t I want an app called Install macOS Golden Gate? What’s InstallAssistant?” In fact, InstallAssistant.pkg is a simple installer that merely puts the Install macOS Golden Gate app in your Applications folder. So, once that file has finished downloading, double-click it and follow the prompts to run the installer, which is really the installer installer. When it’s done, you’ll see Install macOS Golden Gate in your /Applications folder (unless you selected a different location for it). You can then delete the InstallAssistant.pkg file.

An alternative is a command-line program in Terminal. Enter softwareupdate --fetch-full-installer --full-installer-version 27.0 to download the full version.

Once you have it, keep a copy somewhere safe before you run it.

If you used Software Update to download macOS 27 Golden Gate, this section does not apply to you. If you downloaded a standalone installer, bear in mind that if you do an in-place upgrade (whether to your internal SSD or an external SSD), the installer is deleted from /Applications once the process is finished.

I presume the reason for this is that, once macOS 27 is installed, Apple wants to give you back the 21 GB or so of disk space the installer was taking up, since you likely won’t need the installer in the future (and can download it again if you do). But what if you want to install macOS 27 on multiple Macs—or reinstall it later on the same Mac—without having to download that huge installer again? I’ll tell you what: you’d better put that installer in a safe place before you run it! If it’s anywhere else—your desktop, ~/Downloads, or wherever—it won’t be deleted after it runs.

So, before you do anything else, I suggest that you either ⌘-drag the installer to move it from /Applications to another location, or Option-drag the installer to copy it to another location—preferably another volume—so if it is deleted, you’ll have a spare. Or create a bootable installation volume, as below.

Make a bootable installer volume

The macOS 27 installer doesn’t include or require boot media. But you might want to have a copy of the installer on a bootable disk for one of these reasons:

• As a backup, so you don’t have to re-download it if you need it in the future
• To simplify installing macOS 27 on multiple Macs
• To facilitate downgrading to your previous version of macOS should that become necessary, in which case you’d want a bootable installer volume for the old version, not for macOS 27

If none of that applies to you, skip to the last section.

To move ahead with a bootable installer volume, you’ll want a flash drive with at least 32 GB of free capacity. (A 32 GB USB flash drive can be found for under $10 online or at your favorite local electronics store.) Then you follow a simple procedure to put a bootable installer on that drive and, when the time comes, start from that volume and run the installer.

Next, you’ll use a command-line tool called createinstallmedia that is buried inside the installer (and thus is a method that Apple officially sanctions). Using this tool requires a visit to Terminal, but it’s really a matter of copying and pasting one line from Apple’s website into Terminal and replacing the name MyVolume with the name of the drive you’ll be using.

But there’s a catch, in that a bootable installer requires a full macOS installer to work with, and in some cases that may not be what you get when you download macOS 27.

Update your backup

You should already have a complete backup of your startup disk. If you did that just minutes ago—and your backup includes the macOS 27 installer file located outside the /Applications folder—then you can move along to the next step. Otherwise, I suggest updating your backup before running the installer.

With the installer safe, you can run it.

Spotlight

In macOS 27 Golden Gate, Spotlight as such behaves similarly to how it did in Tahoe—though with, Apple claims, more relevant search suggestions. The Spotlight interface has been merged with the Siri AI interface. That is to say, what you see on screen when you invoke Spotlight (via ⌘-Space or whichever custom keyboard shortcut you set) is exactly the same as what you see when you invoke Siri (via the Siri menu bar icon), and you can treat the field in which you type either as a search term or as a prompt. Instead of the former Search, rendered in gray text in the field, it now reads Search or Ask.

As in Tahoe, either before or after you enter a search term, you can narrow the search to various categories. Move the mouse or press the down arrow key to show them; Tahoe, by contrast, used the Tab or right arrow key. You can then click a category or use the arrow keys and Return to select it. Alternatively, you can press the associated keyboard shortcut shown to access each category directly.

Here are the four categories:

• Apps (⌘-1): In this view, only apps are shown (regardless of where they’re located on your Mac). Recently used apps appear at the top, until you start typing.
• Files (⌘-2): Similarly, in this view, only files and folders appear, but that includes apps, too! Again, recent files appear at the top (below Suggestions, explained in a moment) until you start typing.

Results in Apps and Files categories include items on your iPhone, if you’ve set up iPhone Mirroring.

• Actions: (⌘-3): Actions are activities (some provided by Apple, others provided by third-party apps) that you can access directly from Spotlight without opening apps or performing additional steps.
• Clipboard (⌘-4): Spotlight can keep track of things you’ve put on your clipboard previously, including them in search results, as long as this feature is enabled (as it is by default): go to System Settings > Spotlight, scroll to the bottom, and turn Results from Clipboard on or off.

Shortcuts

The Shortcuts user interface was overhauled significantly to steer users away from manually creating shortcuts and toward its major new feature: the Apple Intelligence-powered “Describe a shortcut.” When you click the plus button on the toolbar, you now see a big “What do you want your shortcut to do?” banner.

In the “Describe a shortcut” field at the bottom, type out what you’d like your shortcut to do. Apple Intelligence then takes a first stab at it. You can try out the shortcut and, if it doesn’t work quite right, type a correction in the “Describe a change” field. With any new or existing shortcut, you can select it and click the Edit button on the toolbar to bring up the full Shortcuts editor, which has been rearranged a bit and now includes a Pinned section.

Although the existing interface for creating Automations is still there, a new method is available, too: when editing a shortcut, go to the Automation category in the right-hand sidebar and double-click an automation (such as Time of Day or Message). This adds it to the top of the shortcut so you can configure it while creating or editing a shortcut.

Shortcuts features several new systemwide actions:

• Notification: This action runs when you receive a notification from a specified app.
• Screenshot: This action runs when you save a screenshot to Photos, Files, and/or your Clipboard.
• Store Content, Get Stored Content, and Delete Stored Content: You can now store data within Shortcuts itself, rather than having to create and manage external files.

In addition, there are new actions for several Apple apps:

• Mail: There’s a new Find Message action for Mail.
• Messages: New actions for Messages include Delete Conversations, Delete Messages, Mark as Read, Open Inbox, Search in Messages, and Send Tapback.
• Photos: The new actions for Photos are Auto Enhance Photo, Delete Albums, Delete Photos, Favorite Albums, Find Albums, and Hide Photos.
• Reminders: The Reminders app has new Create Group, Create Section, Delete Groups, Delete Lists, Delete Sections, and Edit List actions.

In addition, some actions have expanded capabilities:

• Get What’s On Screen now lets you specify a data type, such as Images, Text, or Web Pages.
• If now lets you specify multiple conditions, evaluated with Any or All (much like rules in Mail). To add conditions, click the plus button in the If action.

The list of changes in the Photos app is much longer than in any other app, though most of them are small. These are the ones worth knowing about.

• Shared album improvements: When you share an album via iCloud, other participants can now see and interact with it even on Windows PCs and Android phones. In addition, you can “upgrade” your shared albums to show photos and videos at full resolution and enable several other features. To do so, right-click or Control-click an album in the sidebar and choose Upgrade Shared Album; this walks you through a series of steps, after which Photos spends a considerable amount of time—perhaps hours—thinking.

At the end of the process, a Manage Shared Album button appears at the top of the window. Click this to open a dialog with extensive sharing options:

• Permissions: Click the More button next to any participant to change their permission to any of three levels: Can View and Comment, Can Add Photos, or Can Manage Album and Photos. You can also show each person’s contact info or remove the participant, and you can invite new participants.
• Copy Album Link: You can get a link to the shared album and set whether it works for People You Choose or Anyone with the Link.
• Access Requests: Turn this on to permit other people with the link to request access, which you must then manually approve.
• Make Album Temporary: If you turn this on, the album becomes ephemeral, disappearing from Photos after 30 days. To prevent any photos or videos in the album from disappearing too, you must save them to your library first.
• Allow Notifications: Turn this on to be notified when there are changes to the shared album.
• Delete Shared Album: Click this to delete the album completely.

Other devices must be running iOS 27, iPadOS 27 or macOS 27 to use the upgraded features.

There’s a downside to upgrading, though: these higher-resolution shared photos now count toward your iCloud Drive quota, which may require you to buy a more expensive iCloud+ plan.

• New Clean Up: Apple has rebuilt the Apple Intelligence-driven Clean Up feature rolled out in macOS 26 (and on other platforms), and it works substantially better.
• Spatial Reframing: If a photo was taken from an inauspicious angle, you can now adjust the angle, within limits, for a more pleasing effect, thanks to Apple Intelligence.
• Extending: Suppose a photo is cropped too narrowly, or that the subject is off-center. Photos can now use Apple Intelligence to fill in areas adjacent to the area actually captured by generating new pixels that seamlessly blend in with what’s already in the photo.

Both Spatial Reframing and Extending are inventing details, not extracting data from the photo. Be sure you want photo-generated components in your image.

If everything has gone as expected, your Mac is now successfully running macOS 27 Golden Gate. (If things haven’t gone as expected, see what to do when the upgrade goes wrong.) But there are still a few tasks left to do before you get to work—or play—with your new operating system. Here I cover some important initial setup and configuration activities you should get out of the way right now.

Respond to immediate questions

Depending on your starting point, configuration, and upgrade path, you may see a normal desktop and nothing more after installing. In other situations—especially when you have a lot of third-party software—you may be immediately confronted with a large stack of overlapping dialogs and notifications.

Among the most common questions are requests for your user account password or Apple Account password. For example, certain apps may once again need an administrator’s authorization to make changes to your data, and apps that use your Apple Account may need you to sign in again. You’ll also see requests to enable notifications; permit apps to have access to your contacts, calendars, bookmarks, and various resources in System Settings > Privacy & Security—among other alerts.

For example, you may see one or more notifications requesting for permission for apps to access other devices on your local network. This is not suspicious behavior, and it’s fine to allow it.

Work your way through any such dialogs you see, even if they seem redundant or if they ask for permissions you’d previously granted. After that one-time process, most of them will not reappear.

Handle software updates

The next thing you should do is to update macOS itself (and any other crucial Apple software) to the latest version. Sometimes Apple releases bug fixes and security updates almost immediately after a major upgrade, and if any such urgent updates are available, it’s in your best interest to install them right away. (This can be true even if you immediately purchase a newly introduced Mac later this year that can only run macOS 27 and later. Those Macs were “imaged” with the version of macOS 27.0 weeks before they shipped.)

Software Update and the App Store should automatically notify you when updates are available, but I recommend looking at the Software Update pane manually after your Mac starts up under macOS 27 for the first time. Start with System Settings > General > Software Update for updates to macOS 27 itself.

In addition to installing any updates, decide how you want Software Update to handle future updates. Your Mac automatically checks for and can optionally download and even install updates in the background.

1. Go to System Settings > General > Software Update. macOS checks for updates, and any available updates appear. To apply them, click Update Now.
2. Click the Info button next to Automatic Updates. A dialog appears.
3. macOS always checks for updates automatically. Whether it actually does anything when an update is available depends on your other choices here:
   • Download new updates when available, which not only notifies you of updates but also downloads them for you so you can install them as soon as you’re ready. In the notification, click Install to install immediately; click Later and choose Try in an Hour, Try Tonight, or Remind Me Tomorrow to snooze the reminder; or click the notification itself to open the App Store.
   • Install macOS updates, which downloads and installs updates to macOS itself and asks you to restart your Mac. You may be prompted for your password if you change this.
   • Install system data files and security updates, which installs these essential updates without prompting you and without requiring a restart.

For updates to other Apple software and third-party apps you’ve purchased from the App Store, choose Apple menu > App Store. Then click Updates in the sidebar. To update a single app or group of apps, click the Update button next to it. Or, to update all the listed apps at once, click Update All. The App Store downloads and installs the updates automatically. While you’re at it, make sure App Store is set up for automatic updates. In Sequoia and earlier, the Software Update pane of System Settings included an “Install application updates from the App Store” switch. That’s no longer there in macOS 27; instead, it’s right here: go to App Store > Settings and select Automatic Updates.

Deal with other surprises

You may encounter a couple of other peculiarities when first using macOS 27 that cause some initial surprise.

Apple Mail

The first time you launch Mail under macOS 27, a window may inform you that it’s “optimizing” your Mail database. This step should take no more than a few minutes, and is necessary because the macOS 27 version of Mail has updated the database format it uses to store information about your messages.

System Settings

As a reminder for those upgrading from macOS 12 Monterey or earlier, the app formerly known as System Preferences is gone, replaced with a new one called System Settings, which looks quite a bit different. See what changed in System Settings.

Siri and search optimization

The massive overhaul in Siri technology also comes with a complete redo of Spotlight searching in macOS. The new indexing process can apparently take longer—potentially far longer than the previous Spotlight indexing. You might see a note that Siri and Search are optimizing in Settings > Siri or Settings > Spotlight until this is complete.

However, Apple said it would release the indexing update to macOS 26 Tahoe, so that the task would slowly happen over the summer. Then, when you upgrade to macOS 27, the index can be used immediately. I’m not sure how this will play out in practice.

With each new release of macOS, Apple adds, removes, relocates, and renames a bunch of controls in System Settings. macOS 27 Golden Gate is no different, although the changes from Tahoe are quite minor.

To open System Settings, click its Dock icon, double-click System Settings in the Applications folder, or choose Apple menu > System Settings.

As always, it can be difficult to locate a particular setting among the hundreds in System Settings. If you happen to know where a setting is, you can select a category in the sidebar on the left and then navigate to the desired spot on the right. If not, your best bet is to use the Search field, which nearly always shows you what you’re looking for—even if you don’t know the exact name of a feature or setting.

You can see an alphabetical list of all the panes on the View menu; choose a pane to go directly to it.

What follows is what changed between Tahoe and macOS 27, pane by pane, in the order they appear in the sidebar. The Siri pane changed most of all and is covered separately.

Battery settings

Where Tahoe had a Low Power Mode pop-up menu with options Only on Battery, Only on Power Adapter, Never, or Always, macOS 27 instead has two pop-up menus, one for “On battery” and the other for “On power adapter.” For each one, you can choose Automatic, Low Power, or High Power.

General settings

In the AutoFill & Passwords category, there’s a new “AutoFill from” switch, with entries indicating which app(s) can be used to supply AutoFill data. By default, Passwords is the only option (turned on by default), but if you have one or more third-party password managers, they may also appear here.

Accessibility settings

The following categories of Accessibility settings have changes:

• Display: There’s a new “Show borders” switch, which adds borders around toolbar controls, Search fields, and various other interface items to more clearly distinguish their boundaries; this replaces and significantly improves on the previous setting “Show toolbar button shapes.”
• Subtitles and Captioning: This category, which replaces Captions, adds three new controls to fine-tune when and where subtitles/captions appear: “Show when muted,” “Show on skip back,” and “Apply across apps.”

Menu Bar settings

A new “Show suggestions in Control Gallery” switch lets macOS display suggestions when you click Add Controls. Turn it off to remove the suggestions.

Wallpaper settings

As usual, macOS 27 features new static and dynamic wallpapers, and a new screen saver. You’ll never guess which bridge appears in the new images.

Lock Screen settings

A new “Show user name and photo” switch is on by default, giving you the same behavior seen in Tahoe and earlier. But if you turn it off, usernames and photos no longer appear when your Mac is locked, which might be better for privacy in settings where a Mac may be visible to the public.

Keyboard settings

The “Auto-punctuation” switch under Dictation is gone, presumably because automatic punctuation is always on and, according to Apple, greatly improved in macOS 27.

macOS 27 Golden Gate expands the existing Family features parents and guardians can use to restrict their kids’ screen usage, with an emphasis on safety. (You must first enable a Family account and add family members in System Settings > Family.) These new features require that both the parents’ and kids’ devices are running iOS 27, iPadOS 27 or macOS 27 or later; if you haven’t already done so, a message at the top of the Family setting pane reminds you.

These features are described generally rather than step by step, because testing them requires a second device signed in to a child account.

Beyond those features, the Family pane offers a simplified interface that lets parents review their kids’ screen usage time, pause device use, temporarily lift restrictions, or change a schedule with just a few clicks.

Grant per-website browsing permission

For years, families have been able to use the Ask to Buy feature, in which children must have an adult’s explicit approval to purchase apps from the App Store. In macOS 27, this concept expands to include websites. If you enable Ask to Browse for a child, each visit to a website that’s not already approved pops up an Ask to Browse message on the child’s device. If the child requests permission, the parent or guardian sees a request in Messages showing the website in question, along with Approve and Decline buttons.

Ask to Browse works in Safari and other WebKit browsers, but not in Firefox or Chromium-based browsers, which means that any child who can figure out how to download an alternative browser can bypass this feature with trivial ease.

Enforce Communication Safety

Communication Safety is an existing feature that, if enabled, warns children before displaying nude images in apps such as FaceTime and Messages, whether those images are incoming or outgoing. macOS 27 expands this to block violent or gory images, giving the child a way to end the conversation without seeing the objectionable material.

Set time allowances and schedules

Parents now have detailed controls available for restricting when, and for how long, children can use certain types of apps (including games and social media apps). You can, for example, restrict your child to playing games for just an hour a day, or set up a schedule with fine-grained controls, such as “you can use apps A, B, and C before or after school, but only D or E while at school, and F and G only in the evenings.”

At the same time, Apple has given notice that a few features are on their way out: they’re still in macOS 27 Golden Gate, but will no longer be present in macOS 28 next year.

Rosetta

First is Rosetta, the technology that enables Macs with Apple silicon to seamlessly run apps designed to work only on Intel processors. It has been around since macOS 11 Big Sur, but now that the transition to Apple silicon is complete and macOS 27 no longer supports any Intel-based Macs, Rosetta’s days are numbered. Although any apps you have that were designed for Intel processors should still work in macOS 27, you will continue to see the warning messages that started appearing partway through Tahoe’s life cycle.

Technically, it’s Rosetta 2, as Apple had a previous emulation technology called Rosetta. However, Apple’s documentation omits the 2 to refer to this second version.

Translation: you have about a year to obtain a new version of the app designed for Apple silicon (if the developer releases one) or find an alternative. Otherwise, if you depend on that app, you may have to stay on macOS 27 for quite a while.

You can start making the transition from any remaining Intel-based apps now by going to System Settings > General > About and clicking Details under the macOS section. This shows a list of apps and some components on your Mac that have Intel-only code, showing those you used in the last year first.

The built-in tool may not find all the agents, daemons, command-line programs, and other bits and bobs you’ve installed over the years. For that, you should turn to third-party tools that work in Tahoe (and some earlier versions of macOS), like iMazing’s Silicon (free), St. Clair Software’s Go64 (free), and bzwrd’s more elaborate Rosetta Check ($6.99/€6.99 one-time fee).

DVD Player and encrypted HFS+ drives

Similarly, Apple has removed the DVDPlayback framework, which likely means the DVD Player app, which is still present in macOS 27, will be gone in macOS 28.

And, any drives formatted using the encrypted Mac OS Extended (HFS+) format won’t work in macOS 28. If you have such a drive, you’ll want to back it up, reformat it as APFS, and then copy your data back before macOS 28 rolls around in late 2027.

If you’re already running Tahoe, that’s all you need to know for now; the next step is checking your Mac for compatibility. If your Mac is still using an older operating system, there are changes in the past few releases you may not be fully prepared for.

Even if you diligently followed every instruction, you might encounter problems while upgrading. I can’t anticipate every difficulty you may have (or provide solutions in every case), but here are two of the most likely issues and how to deal with them.

When the installation volume can’t be selected

If you run the macOS 27 Golden Gate installer, click Show All Disks when asked to choose a destination, and find that the volume on which you want to install macOS 27 isn’t available, chances are excellent that if you click the volume in question, the installer will usually tell you why it can’t be used and explain how to fix that problem.

When the Mac won’t start up

Following installation, if your machine will not start up under macOS 27 at all, if it gets stuck on a gray or black screen for more than about five minutes, or if you experience a kernel panic upon the first restart, try these steps in order until you are able to start up normally:

1. Force a shutdown and restart: Press and hold the power button for about 10 seconds until your Mac shuts down. Then press it again and wait for it to restart. You should give it plenty of time, as it may be performing a lot of disk integrity operations quietly underneath that black screen—again, five minutes is not unreasonable.
2. Disconnect non-essential USB devices: If your Mac gets stuck on a gray screen and won’t finish booting, try this:
   • Press and hold the power button for about 10 seconds until your Mac shuts down.
   • Disconnect all USB cables from your Mac except any that go to a keyboard, mouse, or other pointing device.
   • Press the power button again and wait for your Mac to start. If it starts normally, you can then reconnect your USB devices. If it’s still stuck after five minutes or so—or if it starts but then you experience a kernel panic—move on to the next step.
3. Try safe mode: Safe mode disables some third-party software and checks your disk for certain types of errors.

To enter safe mode, choose Apple menu > Shut Down and wait until the Mac has fully shut down. Then press and hold the power button until you see “Loading startup options” on the screen. When the Options icon appears, select your startup disk, hold down the Shift key, click Continue in Safe Mode, and then release the Shift key.

If macOS 27 starts up normally after a safe boot, a third-party extension or startup item may be the culprit. Check in /Library/LaunchAgents, /Library/LaunchDaemons, and ~/Library/LaunchAgents for third-party items that haven’t been updated recently (older items are more likely to have compatibility problems).

If you find any that you explicitly recognize and suspect, look for an uninstaller from the developer, and if there is one, use it. If not, consult the documentation that came with the software, or the developer’s website, for removal instructions.

Restart and see whether the problem is still gone. If so, reinstall the uninstalled items one at a time, restarting after each one, until you find the culprit or you’ve installed new copies of them all and your Mac is still working well.

4. Try recovery mode: You can boot into recovery mode by shutting your Mac down and then pressing and holding the power button until you see “Loading startup options” on the screen; when the Options icon appears, click it and then click Continue. A few moments later, you’ll see a macOS Utilities window; that means you’re using recovery mode.

Once in recovery mode, select Disk Utility and click Continue. When it opens, select the problematic macOS 27 volume in the sidebar, click First Aid, and follow the prompts to repair any problems that may have appeared on your macOS 27 volume. Choose Disk Utility > Quit Disk Utility to return to the macOS Utilities window. Then choose Apple menu > Restart.

5. Remove any nonessential hardware: Try restarting with only your Apple-supplied keyboard, mouse, and display attached, and (if you have a Mac Pro) without any third-party PCI or video cards. If this works, check for driver updates, and then reattach the devices one at a time, restarting after each one.
6. Reinstall macOS 27: If you still can’t start your Mac, consider reinstalling macOS 27. Perform a clean install, omitting items in the Applications category when you work your way through the file transfer portion of the installation to eliminate any possibility of software conflicts. (You can add those items later using Migration Assistant.)

In most cases, these steps will lead to a happy macOS 27 installation.

In all likelihood, your experience using macOS 27 Golden Gate will be just fine, and if you’re already using Sequoia, the odds are even more in your favor. However, if you find yourself with an intractable problem that the troubleshooting steps don’t help with and your only choice is to revert to your previous version of macOS, it is possible—though not convenient—as long as you have a full backup.

macOS has no downgrade mechanism as such. All you can do is erase your disk—yes, you really do have to erase the whole thing—and then either restore the whole thing from a bootable duplicate or reinstall your older version of macOS and then separately migrate or restore the data from a data-only duplicate or a Time Machine backup. To erase your disk, you have to start from another volume—the logical options here are a bootable installer for your old version of macOS (see how to make one) or a bootable duplicate. For this purpose, recovery mode won’t work, for the reasons set out at the end of this article.

If you have to downgrade to, say, Tahoe, and you don’t have a bootable duplicate or a bootable installer volume, you’re not necessarily out of luck. While running macOS 27, you can still download the Tahoe installer and use it to create a bootable Tahoe installer volume. The same goes for older versions of macOS.

The process

1. Start up from another volume. To do this, attach the drive containing the other startup volume, go to System Settings > General > Startup Disk, select that volume, and restart your Mac.
2. Run Disk Utility and erase the entire disk, both the system and Data volumes, containing macOS 27:
   a. Choose View > Show All Devices.
   b. Select the topmost icon for the external drive in the list on the left.
   c. Click Erase.
   d. Fill in a name for the new volume, and make sure Format is set to APFS and Scheme is set to GUID Partition Map.
   e. Click Erase.
   f. When the Done button appears, click it. You’ll then have a new volume with the name you entered in step d.
3. Reinstall your old version of macOS. If you already have the installer on your boot volume, you can simply run it; if not, you may have to download it from Apple first using Terminal.
4. Using Migration Assistant at the end of the installation, restore your data from your backup—whether that’s a data-only duplicate or a Time Machine backup—following the Migration Assistant instructions.

Why recovery mode won’t let you downgrade

Even though you can do lots of things after starting in recovery mode—including reinstalling macOS—you probably can’t use recovery mode to downgrade to your old version because recovery mode doesn’t let you install arbitrary previous versions of macOS. Your only option is the most recent version of macOS that will run on your computer: probably not what you need.

In case you were thinking you can restore from a Time Machine backup in recovery mode and use that to get back to your older system…sorry, but no. Although Time Machine used to back up your full startup volume, ever since Big Sur, it backs up only your Data volume, not macOS itself. That’s why a Time Machine backup alone can’t restore an older version of macOS.