Really bad quality of the video

Guys, what's wrong with my camera?:< I've recorded some stuff in 4k quality, on the phone everything looks great, but on pc it looks very very bad. Check the image below. Does it look like 4k? I've downloaded it through icloud. Is there any other way to get videos from phone to pc in full quality? Sorry for mistakes which i could've made but that's my second language. Thanks for help :)

*dunno why but this picture looks not thad bad there, probably cuz of resolution* but i hope resolution aint the answer. I'd like to watch some stuff on my pc:(