How is nextcloud mysql/mariadb encrypted?

How is nextcloud database encrypted?
If VPS owner get into my file config.php - what he can do?
Can he read filenames from database?

Lets say i have webdav on another server, and nextcloud is connecting to this second server in remote storage.
How can i secure this vps to make owner never be able to see my filenames?
(second webdav is sharing on https with htpasswd file and credentials in session)