I have one Plex Drive shared by 2 different Startup Drives on my Mac. I simply want the Plex Drive to be available as my usual Plex Server when I use my secondary startup drive. When I use my secondary startup drive, Plex says my Plex Server is offline.
Are you talking about actual startup drives (each with their own installation of macOS)?
If so… that second OS will needs its own installation of a Plex Media Server. Even if you move the data folders around, Plex is likely to fail with this setup as e.g. because the preferences.xml maintains a machine identifier which will be different between the 2 OS instances.
Have you considered moving the Plex Media Server to a NAS or mini PC (e.g. an Intel NUC) instead?
Yes these are two different OS on two different drives so sounds like that won’t work. I like the idea of Using a Mini PC but since my main computer is just easier at the moment, is it possible to just move my Plex Server from one drive to the other permanently?