I use a TV as a monitor on my PC so every now and then it powers on with a few settings changed (probable due to nvidia driver updates or something like it) and it normally changes the Output color format, from RGB to YCbCr444 or YCbCr420. I’m not going to pretend I understand it, I just want it to look good (to me) so I usually look for this forum post:
https://hardforum.com/threads/chroma-subsampling-where-it-is.2002403
Looking for this image:
I also found this other one
That show it in motion also trying to show more subsampling nuances.