That setting was removed recently due to security concerns. You can still specify an alternate location for your Plex data by following the steps in this how-to:
By default, Plex server stores all its own data on the system drive, in the AppData path of the Windows user.
You might want to change that location, if your system drive is a small SSD or you are simply having capacity issues.
Moving Plex data to a dedicated drive also makes it easier to retain your Plex server data when changing machines or re-installing Windows from scratch.
For larger servers/collections, I recommend a dedicated, internal SSD drive.
Exit/End/Quit/Close plex, using the t…
