@filipfiala I was finally able to get transcoding working on my J6413.
What worked for me:
Add --device=/dev/dri to Docker container's Extra Parameters.
Add i915.enable_guc=2 kernel parameter (Main > Flash > Syslinux Configuration - My 2nd line looks like this: append initrd=/bzroot i915.enable_guc=2)
Enable low power encoding in Jellyfin (Enable Intel Low-Power H.264 hardware encoder & Enable Intel Low-Power HEVC hardware encoder)
Disable VPP Tone Mapping (You can still use OpenCL)
Unraid 6.12.4
Jellyfin 10.8.12