I couldn’t make things easy for myself when I migrated, because I wanted to use postgres, while the snap uses mysql/mariadb and I wanted S3 storage instead of file system.

In the end I just pulled down all the user filed and exported the calendars and contacts manually, then imported them on the new instance.

There are some blog posts on migrating db types, but my install is very minimal and I just didn’t want the headache.

If you don’t want to change the database type, then you can just dump the db from the snap, backup the user file directory, then restore into the new database and rsync up all the files.