you mentioned you’re using mysql as opposed to our mariadb container; did you verify your mysql instance is allowing remote connections? By default this isn’t allowed. it does make it a bit more challenging since we know the issue is on the database side but you’re not using our database, presumably because your mysql instance is on another server it looks like.
Have you tried just connecting? mysql -u bookstack_admin -p -h 192.168.0.105 input your password and show databases; (you should see bookstack)