Are you absolutely sure that you have the i915 firmware installed and enabled?
If you have gone through these steps of adding the modules: https://jellyfin.org/docs/general/administration/hardware-acceleration/intel/#low-power-encoding
and it doesn’t work, you may have to manually download the git linux firmware library, extract the i915 folder and place it in your firmware folder.
That is how I got jellyfin working on my A380 after pulling my hair out about it.
Please check and post your dmesg starting up.
You should see GUC and HUC enabling.
Yep, it is also worth to note that 6.9 rc6 (iirc) fixed this issue, and mainline 6.9 should have this issue fixed.
Apparently fixed by adding 1 = sign 😁