That’s challenging to answer without more details about your installation, such as that asked for in the support template.
However, you may find the Maintenance chapter of the the Admin Manual useful. It covers backups, restoration, server migrations, etc.
There are at least three places that contain data you may care about:
- your database (within MariaDB/etc)
- your config (
config/within the Nc installation folder) - your files (located with the
datadirectoryspecified in yourconfig/config.php)