I have used this as a guide for backing up and restoring plex on my Synology NAS:
https://forums.plex.tv/t/move-backup-plex-media-library-in-synology-nas/572289/17
Thank you, @trumpy81.
Just curious, why skip the preferences file? I have left it in and it restores fine. Without it, I find I have to reconnect the server as if new, leading to duplication issues in third party situations (e.g. Tautulli). I can fix these duplications, but curious about why we should exclude the preferences file in the first place?