I'm not exactly sure how these sites work, but they're clearly doing something different from "regular" upscaling like what happens when you just make a picture

I'm not exactly sure how these sites work, but they're clearly doing something different from "regular" upscaling like what happens when you just make a picture larger and blurrier, it looks like some kind of semi-vector type conversion before the resizing, but it's never described beyond the regular AI/ML buzzwords. The reason I ask is because it could be really useful for stuff like wallpaper resizing where the only thing you really want is for the larger size to look decent, not necessarily be exactly like the original.