How do i restore the sql-dump?
Theoretically if you create the NextCloud data directory /mnt/dietpi_userdata/nextcloud_data manually and store the SQL dump named as dietpi-nextcloud-database-backup.sql inside, it should be restored automatically on new installation.
what would happen, if external mounted drives were changed? when i mount them to same /mnt/directory is it ok?
Nothing should happen if the new drive contains the very same data and is mounted to very same mount point.