I just found this post:
https://www.reddit.com/r/unRAID/comments/1tbnlfx/730_stableintel_arc_310_hw_transcoding_stopped/

I am on 7.3 RC1, and I was not aware about it until now, this user is correct, ARC card doesn't work, in my case it is A380.

It is detected in the system, but Unraid does not read anything from it (intel_gpu_top returns igpu only). I have set it in plex as transcode device and it does fall back to igpu.

Immich fails to use GPU as well got errors in the log when it is trying to use it for AI.

Device is listed under System Devices.

Please see attached Diagnostics.

arrakis-diagnostics-20260513-0713.zip

For top you need to specify the cardwith intel_gpu_top -d pci:slot=0000:04:00.0 for the A380

A380s work in 7.3 https://forums.unraid.net/topic/89453-plugin-gpu-statistics/page/84/#findComment-1621914

04:00.0 VGA compatible controller [0300]: Intel Corporation DG2 [Arc A380] [8086:56a5] (rev 05)

Subsystem: Sparkle Computer Co., Ltd. A380 ELF [172f:3943]

Kernel driver in use: i915

Kernel modules: i915, xe

05:00.0 Audio device [0403]: Intel Corporation DG2 Audio Controller [8086:4f92]

Subsystem: Sparkle Computer Co., Ltd. Device [172f:3943]

It does work now, it looks like GPU group changed and immich could not access it anymore, after adding immich to the new GPU group all is running well.