For whatever it is worth to you I've hardened my jellyfin docker compose this way. I'm obscuring some things in this that are local to my network.

The container is read only. It mounts the media read only. It should be fairly isolated from getting privileges it shouldn't have. The only things lost in this setup are the ability to delete media from a jellyfin client (something I never do) and the ability to manipulate files directly stored with the media. I use bazarr for subtitles so don't need jellyfin to download them and I don't keep trickplay or any other jellyfin metadata related files alongside the media. I feel pretty confident with this that even if the jellyfin codebase had a serious 0 day that the worst I'd lose is metadata and server setup, and important config files I have backing up to another machine.

I'm sure there's things I've overlooked with this setup so I'm very open to being told there's a better way to do something.

services:
  jellyfin:
    image: jellyfin/jellyfin:latest
    container_name: jellyfin
    restart: unless-stopped
    user: ${PUID}:${PGID}
    group_add:
      - "992" # my render group id
    security_opt:
      - no-new-privileges:true
    cap_drop:
      - ALL
    read_only: true
    networks:
      macvlan:
        ipv4_address: OBSCURED
        mac_address: OBSCURED
    healthcheck:
      test: [ "CMD", "curl", "-fsS", "http://127.0.0.1:8096/health" ]
      interval: 1m
      timeout: 10s
      retries: 3
      start_period: 30s
    environment:
      - TZ=${TZ}
      - JELLYFIN_PublishedServerUrl=OBSCURED
      - TMPDIR=/transcode
    volumes:
      - ./jellyfin:/config
      - ./cache:/cache
      - ${MEDIA}:/media:ro
      - ./transcode:/transcode # be sure to set this dir in the jellyfin config
    devices:
      - /dev/dri/renderD128:/dev/dri/renderD128
    deploy:
      resources:
        limits:
          memory: 5G
        reservations:
          memory: 3G

  watchstate:
    image: ghcr.io/arabcoders/watchstate:latest
    container_name: watchstate
    restart: unless-stopped
    user: ${PUID}:${PGID}
    ports:
      - 8180:8080/tcp
    volumes:
      - ./watchstate:/config

networks:
  macvlan:
    driver: macvlan
    driver_opts:
      parent: OBSCURED # Replace with host network interface name (find via: ip route | grep default)
    ipam:
      config:
        - subnet: OBSCURED # Your local LAN network CIDR
          gateway: OBSCURED # Your local router IP address