The two screenshots are hilarious to me, I cannot verify the information shown since I do not have one but the one done with the ATV 4K 2017 shows that YT is not even sending an UHD ("4k") video file to the ATV to output - maybe an Apple SoC performance issue when having to decode VP9 in software*?
Again, I don't understand how this hasn't lead to a public "sh**storm" considerung what stupid things in the past actually did.
*I'm also pissed about the outdated A12 SoC in the ATV 4K 2021, not because of gaming stuff (not my cup of tea) but to have room for future features like maybe being able to decode UHD-HDR AV1 in software which is an intermediate destination coming pretty soon.
It seems the ATV 4K 2017 isn't even able to decode 4K YouTube video files in real-time due to Google's video codec or Apple's SoC video codec feature set choice. The 2021 model on the other hand can at least do that so I guess you'll have to wait till 2025 to get HDR! 🤣