Maximum execution time errors mean PHP stopped a script at its time limit. The number in the message tells you who set that limit: 30 is usually PHP or your host, while 300 or 600 means WordPress raised it.

The missing the MySQL extension message means PHP cannot find the function mysqli_connect, so WordPress stopped before it touched your database. Check the PHP version and the extension list for the account, choose one MySQL driver set, and reload. Plugins, themes and wp-config.php are not the cause.

The active theme is broken means WordPress already switched your site to a default theme. Restore the missing folder or file first, then reactivate your theme.
