An automatic new installation will always go into a database container.
What you can do after, is:
- create a DB backup
- disable the DB container, in docker-compose.override.yml
- configure an other DB in header.inc.php
- restore the backup via our setup
What you lose is the optimal DB version we recommend. For 21.1 it’s currently MariaDB 10.4, for 23.1 it will probably be 10.6.
Ralf