Just make sure you have selected the “Enhanced” format on whichever port you have connected the ATV.

Monoprice certified high speed cables should be fine.

A movie has to be available in DV to be played in DV. If you go to Disney+ and watch something like Bluey, you won’t see it streaming in Dolby Vision.

At minimum, get a certified premium high speed cable, and it should be good enough. Certified ultra high speed will work too, but not necessary.

Do you use any streaming services like Netflix, Disney+, etc?