One of the new tvOS 14 features Apple released was support for YouTube 4K video streaming, but tvOS 14 Apple TV 4K users noticed that support was not available. Apple has gradually opened access to the expected feature according to the situation.
Apple TV YouTube application has gotten the expected feature!
On Reddit, a user named Flatpannels HD posted footage of 4K YouTube videos. Multiple users then reported seeing 4K playback options in the YouTube app on tvOS 14, tvOS 14.0.1 and tvOS 14.2.
4K support is not yet available to all users, for now most users can still watch 1080p video. Although 4K content appears to be available, those with access still cannot enable HDR and 4K videos are limited to 30 frames per second.
It is unclear whether the lack of HDR is temporary or is a limitation on the 4K Apple TV. It is also unknown when 4K content will be available to everyone. It seems that a new tvOS 14 update will not be expected for the feature, which is thought to be gradually widespread.