Gah; I can't get mine working! I can see the listing in /dev/dri -> ls, did a modprobe i915, added the /dev/dri to devices in the settings. When I used "docker exec -it plex ls -lh /dev/dri" in the console, it returns both my iGPU as well as my PCIE GPU:
Still, it doesn't work off the iGPU and instead continues to software transcode. I made sure to as well establish the transcoding is enabled in Plex.
For context, I'm using the ASRock C236 WSI paired with the i7-7700K, with my 3060ti thrown into the PCIe slot.
I assume that the iGPU does exist and is usable, since I went ahead and installed Handbrake and added the /dev/dri to its devices. It does show it as an option in the Video Encoder: