I recently made my first TrueNAS build. It was mainly for Plex Media Server, the problem is I can’t make it use the iGPU for transcoding. It is supposed to use it without any further setup but mine uses the CPU to transcode.
You will need to contact the TrueNAS package developer for support.
Specifically, CometLake CPUs need Intel Compute Runtime ver 21.49.21786 QSV and tone mapping.
(they are the ones who created the TrueNAS package)
You will be hard pressed to get up to date HW support with TrueNAS CORE as its built on top of FreeBSD. I suggest you look into the Debian based TrueNAS SCALE
I could set it up now, and in the jail there is the /dev/drm and /dev/dri folder. But now when it has to transcode the whole server crashes and restarts