I personally use the QNAP container station. However, have you tried going through the official documentation on how to add the Docker package repository on Ubuntu?
Below is my Docker Compose file I use to run my Plex container. @gregology provided another example above if you rather start directly using the docker command line.
As far as the NVIDIA configuration in my setup, this is only necessary to support hardware transcoding and should probably not be needed to troubleshoot this issue.
version: '3'
services:
plex:
image: linuxserver/plex
container_name: plex
network_mode: host
restart: always
devices:
- /dev/nvidia0:/dev/nvidia0
- /dev/nvidiactl:/dev/nvidiactl
- /dev/nvidia-uvm:/dev/nvidia-uvm
volumes:
- ./data:/config
- /share/Multimedia:/data
- /dev/shm:/transcode
- /opt/NVIDIA_GPU_DRV/usr:/usr/local/nvidia:ro
environment:
PUID: <docker-uid>
PGID: <docker-gid>
VERSION: latest