Late reply here but the solution marked in this post throws an error whenever there isn’t an entity_picture attribute available. The following should fix that.
- platform: generic
name: Android Now Playing
still_image_url: http://10.0.20.3:8123{{ state_attr('media_player.android_tv', 'entity_picture') }}
This is assuming that in the AndroidTV integration (or DebugBridge as it is now called) the option to acquire artwork via screenshots is set to CHECKED. Correct ?