this article explains why messages deleted on iPhone are not deleted on Apple Watch and what to do to fix the issue.
The Apple Watch is the ultimate wearable tool to help keep you abreast of your messages, phone calls, activity, and more. When it works, the Apple Watch is great, but when it fails, the wearable can Prove to be quite annoying.
One area that has annoyed users for years is Messages.
For some people, text messages do not sync accurately across devices. Consequently, text messages deleted on the iPhone may still show up on the Apple Watch.
People have complained about messages not deleting from apple watch when deleted from iPhone for nearly two years.
As far back as watchOS 5, a couple of users have stated that SMS messages deleted on their iPhone are not deleted on their Apple Watch.
Why are messages deleted on iPhone not deleted on Apple Watch?
It’s not a problem with iCloud as these deleted messages do not show up on the iPad or the Mac. It’s an issue that seems to be specific to the Apple Watch.
Some users believe this is how Apple designed Messages to work. That if you write an SMS message from your Apple Watch first, then it won’t get deleted. If you composed the message on an iPhone, then it will be deleted across devices.
Other users argues that even if you have Messages enabled in iCloud, the OS will only delete iMessages and not SMS messages.
Currently, the only way to get rid of these orphaned messages on the Apple Watch is to delete them manually.
Unfortunately, it seams there has been no progress over the intervening years to resolve this issue. Even the Apple Watch Series 5 on watchOS 6 has this problem. Some users have given up hope that Apple will fix messages not deleting on Apple Watch issue.