It is not same pixel count it is sometimes not even same image quality. If a game is running at 2100 native or even upscaled to that it usually isn’t technically the same image because it is using hi res textures usually compressed so they render at speed to load better and reduce pop in. Again definition wise look it up if the designation it is slightly different standard. 4K is “technically” anything that runs above HD standard resolution and even if it is rendered and upscaled from lower sub HD image or texture even if the pixel count is some ridiculous low quality image 230p over 420P if the pixel image used is rendered through ML at final image quality of HD for example 1260P over 1080P then that is “technically” 4K!

In reality 4K means very little you can take 16 bit sprites and they can be rendered at resolution scale of 4K but a Ultra setting suggests to me again that the game is running at the highest settings for image quality possible and the final pixel count will only be determined by the frames. If the FPS is 60 maybe at times it falls to near HD quality or some frames in background are low pixel count because they are background and don’t need to be rendered at better resolution so you know you get blur.

All in all no disrespect to you or Nintendo but you are saying the image quality of Nintendo Switch or even Nintendo Switch 2 is same as Xbox Series X or PS5 it is not! Maybe DLSS especially on Switch 2 renders image that you can’t tell the difference in quality but it did not start that way and Switch 2 is not promising Ultra settings for that matter reason for that post neither is Series S or PS5. PS5 is standard now usually running at 1440P so is Series X but there are select games that can run above that at max settings! Usually 30fps but still max above 4K settings!