SOLVED: Intel Arc A310 won't transcode

[Playing4Peanuts]

I'd bet that you did not have any 6.12 kernel headers installed.  The i915 driver is built into the kernel, but the kernel HEADERS are what allow Jellyfin to interface with Quick Sync.

Yep I'm betting thats what it was. They were installed with the proxmox kernel. I read somewhere that these are not included in the backported debian kernels for some reason. Thanks for your help!