So for the longest time I’ve been annoyed with black flashing whenever I’m watching YouTube videos or shorts on my AppleTV. I assumed this was related to the black screen between videos, but it turned out this assumption is wrong! I had set the default output to 4K Dolby Vision, and to adjust to content, but that’s sub-optimal. There is no need to run all your menus and such in Dolby Vision. Instead, set AppleTV to use 4K SDR, and it will automatically turn on Dolby Vision whenever your content supports it. TIL. (Source)