Apple

This is necessarily “cool” but, to me, necessary if you want the best/most accurate picture throughout apps:

Your instinct will be to accept the highest quality setting the Apple TV gives you, like 4K HDR, for example. Don’t! That will default everything to 4K HDR, even if the content is SDR. 4K SDR and match content and frame rate ON is generally accepted as the best way to mostly ensure you get SDR when you should and HDR when you should (so long as the app itself supports auto-switching.) if it doesn’t support, you can always do a one-off manual toggle.