iMessages on Apple Watch
My wife and I share our Apple ID. How do I stop receiving her iMessages on my Apple Watch?
Apple Watch Series 8
Question marked as
Stop sharing the same Apple ID. You each need your own personal ID, which you can link with Family Sharing
What is Family Sharing? - Apple Support
Unfortunately there is no practical way to unravel the existing messages. One or both of you will get a new ID, but the message history from your sharing era will for ever be shared.