Settings - 'show advanced ’ - [server name] - Manage - Troubleshooting
“Download Database”
This will give you a copy of the primary Plex server database file.
It won’t contain any posters, or thumbnails, nor the results of the most complex analysis in Plex like thumbnails or sonic details of your music.
But the main structure of your libraries will be in there.
If you can implant this file into a new installation, chances are that you can use it to reconstruct your collection.
On a new setup, you will need file access to the Plex data folder.
Unfortunately I cannot help you with that, as I have never used an Asustor NAS device.
https://support.plex.tv/articles/202485658-restore-a-database-backed-up-via-scheduled-tasks/
https://support.plex.tv/articles/201539237-backing-up-plex-media-server-data/
You could also open this database file with an SQLite database editor, then glean some information about the file names and the folder path of your media files.
You will need to reconstruct these on a new Plex server setup. The database editor allows you to even change these references directly, if they cannot be reconstructed perfectly in a new setup.
