I'm getting the exact same thing, which has taken down nextcloud obviously. When I tried to login in I get :
EDIT:
And just like the above, deleting mariadb completely along with the appdata folder, restoring from my last CA backup a few days ago, and then reinstalling the docker container while pointing it to the restored appdata folder fixed the issue.
Thank god for backups, but I really shouldn't had have to use it just because of an update....