sorry to resurrect an old post, but from my understanding of what OP was looking for was to run a jellyfin server on the same box as libreelec.
after many attempts I was able to get it working, and although I do not know if I will miss some details here I'll give you the short version, for anyone else that wants to do this.
I installed the Linuxserver.io repo some time ago, and they have a jellyfin docker container.
the problem I ran into, was that I could never get logged into jellyfin because root access is disabled, and libreelec uses root for most everything.
after countless hours, many attempts and scouring the forums, I stumbled across a post talking about SMB, and that there is an account called nobody.
I looked in the /etc/passwd, which contains basic information about each user, such as the username, user ID (UID), group ID (GID).
in the jellyfin docker configuration, I changed the corresponding UID/GID to "nobody"
rebooted, just as a precaution but it probably would've worked by just starting the docker.
and then I logged into the web interface as nobody with no password.
I was then able to set up users inside jellyfin.
I hope these breadcrumbs help someone else
