Are both of you chmod-ing the /dev/dri devices? If that is the case, the proper solution is to add the user running the LXC to the render group. That will persist between reboots.
Jellyfin 10.10.3 (Docker)
Ubuntu 24.04 LTS
Intel i3 12100
Intel Arc A380
OS drive - SK Hynix P41 1TB
Storage
3x WD Red Pro 6TB CMR in RAIDZ1 (JF Library)