

user and PUID, PGID do the same thing and not all images support PUID and PGID. They tell docker to run the image using the user with those id. My user has ID 30000 and group 30002. This allows me to change files on my library with this user without causing permissions issues for jellyfin.

Investigate what? That is a standard config and didn’t change anything. Your Raspberry Pi is maybe more powerful than my server. How big is your library?