I am logged into the iCloud account and Messages.app was working on another macbook pro for me. This one is missing something.
The "@iMessage" panel shows the correct information
But on "General" if clicking on "Set up name and photo sharing" I see:
Sharing Name and Photo is not available because iCloud and iMessage accounts are different or are not signed in
What else needs to be done here? This is an older 2015 laptop on Big Sur.
Best Answer
This may be only a partial answer but it does allow to set the name of the linked messages user.
It is necessary to configure the "Apple ID" configurator in System Preferences.
It is a complicated ordeal to configure it seems. I am partially through that configuration. Messages are still not synchronizing from iCloud.
Update Messages are now getting synchronized. I think the additional piece to the puzzle is to completely logout or reboot.