You only need to open port 8096 in Ubuntu to allow for local access. You don't need to change anything in your router. Routers, by default, block all unsolicited requests unless you port forward.
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)