Are there any logs named "ffmpeg.transcode" or something similar. All your playback attempts are requiring transcoding. Is your server an Intel Mac Mini or an M1/2 Mac Mini?
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)