The admin settings page is bypassed on install so the next time the settings page is loaded undefined offsets are thrown as the defaults haven't yet been set.
Warning: Trying to access array offset on value of type null in /var/www/moodlemysql/lib/adminlib.php on line 4053
Warning: Trying to access array offset on value of type null in /var/www/moodlemysql/lib/adminlib.php on line 4059
@sarahjcotton can you please include the full undefined offset error messages here - helps with others google searching an error, but also with the PR process to ensure the code is going in the right place.
The admin settings page is bypassed on install so the next time the settings page is loaded undefined offsets are thrown as the defaults haven't yet been set.