Maybe some packages of mariadb is missing/deleted by the OS while doing some upgrade or update actions
If the problem is still unresolved, I will suggest you to reinstall mariadb (be careful while doing this as its sensitive…if anything wrong happens, your mariadb will be down and thus all your sites). Better you take snapshot of your whole server before trying this for safety.
Follow this method: Upgrading MariaDB manually - #3 by nick.chomey