Reinstalling / resetting would be a waste of time and only compound the problem.
This is a simple case of granting permission for “System Internal User” PlexMediaServer (which runs a service user) permission to see the shared folder and All subfolders and files everywhere you have media.
The How-To shows you how to set the top permission then propagate it down into all the subfolders and files (necessary)
Lastly, external drives appear as shared folders. It seems strange but doing it that way means one rule applies to everything
