Video works in Jellyfin Web but not on Android (fire tv included)

[lx77]

The server is a synology DS416play with an Intel Braswell Chip.
Yes, it is a docker install.

I installed it with portainer.

Code:

version: "3.9"
services:
  jellyfin:
    image: jellyfin/jellyfin:latest
    container_name: Jellyfin-HT
    environment:
      TZ: Europe/Berlin
      user: 1026:100
    volumes:
      - /volume1/docker/jellyfin/config:/config:rw
      - /volume1/docker/jellyfin/cache:/cache:rw
      - /volume1/docker/jellyfin/logs:/logs:rw
      - /volume1/video:/video:rw
      - /volume1/music:/audio:rw
    devices:
      - /dev/dri/renderD128:/dev/dri/renderD128
      - /dev/dri/card0:/dev/dri/card0
    restart: on-failure:5
    network_mode: host

Did I miss anything?

My transcoding settings are like…
   

Isn't it strange that it works in Jellyfin Web but not on android?