Are you talking about VR videos or 2D?
For VR videos you want to watch minimum 6K quality, preferred 8K
Keep in mind, if a video is advertised as 8K that doesn't mean it is 100% going to be very good quality, some studios will upscale and it'll look like ass. Also camera distance & lighting matters a lot here
For live cams, 6K is currently the max quality. Lighting makes a huge difference
(I think, unless something changed) SLR Originals are always going to be 8K max quality if you want something to compare to. Also keep an eye on when a video was uploaded, camera technology progresses as well as upscaling advances