To see what content the ATV4k plays, swipe down from the top of the remote control.
But you run ATV4k errors …
Best practice is to set apple tv to 4k SDR and then turn on frame rate and dynamic range matching.
Make sure that in the corresponding sub-section no mode is verified.
When you play HDR and Dolby Vision content, it will switch to output them, but will broadcast SDR otherwise, which will mean SDR content will look more proper.