Upscaling to 4k just copies and adds pixels next to existing pixel to make the image bigger. Sometimes upscalling makes the image look worse even. blurry.
Upscaling sometimes resamples images. It's just just a "closest neighbour and then some" duplicating, you have directional gradients, multidirectional gradients, all sortsa bullshit.
I notice the 4k difference in blueray movies but not much in games. But the HDR is noticeable in games. I'm on a 4k 120hz Tv and Series X. I imagine games will get better tho.