Messages not syncing between iPhone and Mac mini?

I have a Mini M4 which is okay but in the last few days it no longer syncs with my iPhone - I can have 6 new messages on my phone and no '!' or number on my Mac. It also looks like my Mac isn't even picking up the messages which seems like the sync no longer works even though it is on. Running Sequioa os.

[Re-Titled by Moderator]

Original Title: Messages and Mail don't sync