Since this is a NAS, you have to adjust permissions on the NAS side. AFAIK, whatever you do from the client perspective won't adjust permissions how you think it would if it were a local drive.
Jellyfin 10.10.5 (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)