Over the last 3-4 weeks I have seen a lot of isses with ADD-joined computers upgrading to 20H2.
After upgrade they have lost the ADD association, and just asks for a local credential.
But as the computers have been set up for the end user on ADD directly, there is not local users.
I only remidy has been to unlock the local administrator using some kind of command line tool and the rejoin ADD. When I do that everything looks fine, but it can be a pain with users in remote locations :)