Check the logs for the MySQL container. Perhaps it’s an old MySQL 5.6 install that has been upgraded to MySQL 5.7 but mysql_upgrade hasn’t been run? It has to be done manually there - see Xibo CMS 2.3.10 Released - #2 by alex
Once you get on to 4.0.15 you should check the notes about the upgrade from MySQL 8.0 to 8.4 too. See MySQL 8.0 - 8.4 Upgrade Notes (mysql_native_password)