You might want to look at PSA: Script to back up and restore Plex app data on a Windows system
If you want to gift yourself the luxury of a separate drive for the Plex metadata, you could perform [HowTo] An extended guide on how to move the Plex data folder on Windows
and backup the registry again.
after reinstalling Windows, make sure the plex data drive has the same drive letter as before.
Then install Plex server,
close it
import the registry backup
reboot
