imessage asking to login to apple account and not working
Upgraded to Big Sur and iMessage is asking to sign in with apple id for iMessage and it will not work. What if any resolution is there?
Do you have a Time Machine backup to Restore to/from?
https://support.apple.com/guide/mac-help/revert-to-a-previous-macos-version-mh15216/mac
If not…
Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode?
Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.
To find out if it's system wide or user specific, try this...
Open System Preferences>Users & Groups, unlock the lock, click on the little plus icon, make a new admin account, log out & into the new account.
Does it work in the new account?