Additionally to the whole contents of the Plex data folder, you need to salvage the old Plex Registry branch. There are guides out there how to do that with a registry of a defunct Windows installation.
Keep in mind that you will need to adapt the structure names in a .reg file which was exported from a foreign registry hive.
- https://support.plex.tv/articles/201539237-backing-up-plex-media-server-data/
- https://support.plex.tv/articles/201370363-move-an-install-to-another-system/
Avoid moving the old plex data folder into a zip (or other) archive. If possible, copy it directly to the new location (using robocopy /MIR for instance).
Check the access permissions of the copied folder structure. The Windows user account which is used to run Plex needs full access to it.
Then import the registry backup file on the new Windows installation – but DON’T run Plex server yet.
Instead, create or modify the registry key which tells Plex where to look for its Plex data folder, according to [HowTo] An extended guide on how to move the Plex data folder on Windows
All media sources need to be available at their “old” addresses/locations (i.e. like they were in the old Windows installation. Restore drive letter assignments or UNC network paths as they were before, if necessary.)
Verify that this is the case before the first start of Plex server.
