I am currently running Ubuntu 20.04.2 on a non 4k screen and average hardware. A few months back I had Windows 10 and tried to play a 4k video in it. As expected, it was playing choppy.

I updated the outdated VLC and tried again. This time the video was playing smoothly. I also installed MPC, and the 4k videos were playing just fine it that too.

Fast forward to the present day. I tried the same thing with VLC. It plays all choppy with full of gray glitching screen. Tried all the online solutions to fix this, none of them worked. I downloaded a different 4k video, but same result. I tried playing these videos on my phone (which supports 4k) and they play fine.

Now don't give me "It's because your hardware doesn't support it" because I have played 4k movies on this same desktop months ago when I had Windows and there were no problem. I'm facing this only on Linux this time.