Yeah, Truenas goldeye can load the firmware, including the GuC and the HuC, so the card shows up in plex now, but the console will spit out an error when it tries to transcode with VAAPI because the version of ffmpeg they are using is not compiled to support the bleeding edge of intel media driver for linux. After the error happens, plex falls back to software encoding. At present, it appears the ball is in Plex’s court for updating ffmpeg and getting it compile with the latest and greatest intel-media-driver so they can support Battlemage’s generation of cards.
If you really want battlemage support right now, you can always run plex server on windows. Till then, we need to wait for plex’s team. Luckily, they are actively working on it.