My instance levels out at around 2.5GB and stays there. During big library scans where I add a bunch of new media it climbs to 4-6GB from the ffmpeg processes it spawns, but Jellyfin itself stays at 2.5GB.
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)