What display is he using, projector, LED or OLED? Is he setting his ATV manually? I just did so myself and the results are still negative in regard to playing back 4K/Dolby Vision.
IIRC, @JohnRice has a Visio (and/or Hisense) something LED... unless he recently sprung for an LG OLED while I was paying attention...
Hmmm... John, didn't you used to list your A/V gear in your HTF signature and/or profile?
_Man_