You need to set a password for the account first. Then it will prompt on the first login. I'm not aware of a way to make it prompt for a PIN for subsequent logins.
Jellyfin 10.10.7 (Docker)
Ubuntu 24.04.2 LTS w/HWE
Intel i3 12100
Intel Arc A380
OS drive - SK Hynix P41 1TB
Storage
4x WD Red Pro 6TB CMR in RAIDZ1