I invited a friend to my Plex server home and granted them access to my libraries. When they installed the Plex app on their gaming console and phone, they were able to connect without me entering a code into https://www.plex.tv/link. They are able to watch videos from my library, but I can’t see their device Settings->Devices. However, if they are watching something, the device name is shown under Status->Now Playing. Any idea why?
That is perfectly normal.
Under Devices, you only see devices and clients which are signed in to your ownplex.tv account.
You cannot manage other user’s devices.
You should think twice before adding other persons than your immediate family into your Plex Home.
Because Plex Home has ‘Fast User Switching’, which enables any member of the Home to easily switch to your account, if they guess your 4-digit PIN right.