I finally found a solution in the Plex forums: https://forums.plex.tv/t/raspberry-pi-omv5-and-plex/658872/3
I used the tag :bionic for the image, instead of :latest and now it works correctly.
I have also seen that Plex propose a solution to use its own Docker image for ARM https://github.com/plexinc/pms-docker
The provided docker-compose
templates use the plexinc/pms-docker
image which is the amd64 build and won’t work on ARM devices.
docker-compose with ARM devices, you must first build one of the ARM images locally.
docker build -t plexinc/pms-docker:latest -f Dockerfile.armv7 . # or arm64
Then you can