How did you get the Apple tv 4k to display Dolby digital instead of Stereo?
What techniques did you use?
Question marked as
In order to output at the best compatible format it should be set to auto, but that also means it needs to be connected to eARC as it uses Dolby MAT and that needs more bandwidth. Otherwise, you will only get stereo unless you force it to Dolby 5.1 (Settings > Video and Audio > Audio Format and turn on Change Format)