OK. So in your opening post the bit rate is 120Mbps. Is that coming into jellyfin? Or going out of Jellyfin? From the ffmpeg log it looks like that is the output bit rate?
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)