I use Plex primarily on TrueNAS as an App. I can never easily tell if it is using a GPU for transcoding. It would be nice if there was a test in the settings of the server to just click a button have it try to run a simple GPU transcoding and report that, yes it works or no, it’s broken. Is there some easy way to test this that I’m not aware of?
https://support.plex.tv/articles/200871837-status-and-dashboard/
will tell you if a currently running transcode is using hardware (for decoding and encoding separately)