they shoot in 8K? I am sitting 1m from a 42.5" 4K screen. It has 4 pixels/mm (104dpi), i also have a 27" 4K screen with 208dpi that i can sit 0.5m from. I cannot see the pixels on a 4K screen. I would argue that youtube should limit it's output to HD unless the user asks for 4K. I cannot tell the diference between 4K and HD when I am sat 1m from the screen and the only reason i got a 4K screen was so that fonts would be smooth. Why even bother to shoot a youtube vide in 8K? at 4x the required datarate, oh I suppose it's some stupid fps rate as well. But I guess it's bragging rights and that attracts and audience - wow must match this channel is was shot at 4x the resolution and 3 times the frame rate my eyes will appreciate or my hardware can work at but sure it makes a difference.
For what I read, since I don't understand anything about video, most of people using the 8K cameras do that and then downsample the video to 4K. For what I read, again gives more info regarding the average of the colours in the pixels.
It's also used to crop and reframing, so basically they shoot 8K and crop what they want into 4K.
Again regarding what I read and listen, don't have any experience with video editing. And to be sincere after 4K I don't note any difference. The biggest I note is in close ups to a face of a person, you can really see the texture of the skin of a person and hairs in 4K compared with 1080p.
Still I note more difference in resolution in Animation, specially Anime/Computer FX Movie from 4K to 1080P that real life actors. In my honest opinion, 1080P in a good OLED TV with HDR multi zone looks way better that Normal 4K in IPS screens, correctly calibrated to DCI-P3