A key component is that when a game generates pixels, it also generates other data. Such as a Z-buffer for pixel depth and motion vectors (for motion blur, among other things). Feeding this to the upscaling algorithm vastly improves image quality.
The larger problem to solve with these upscalers are temporal artifacts when using the above information. This lead to a number of heuristics, but if you train a neural network to do the work, it tends to perform better than the heuristics. There's still a ton of research going into non-ML solutions however, because the current console generation doesn't have AI-acceleration available, nor does a lot of hardware out there. So there's some longevity to be had by doing a good job for all that hardware out there.
The larger problem to solve with these upscalers are temporal artifacts when using the above information. This lead to a number of heuristics, but if you train a neural network to do the work, it tends to perform better than the heuristics. There's still a ton of research going into non-ML solutions however, because the current console generation doesn't have AI-acceleration available, nor does a lot of hardware out there. So there's some longevity to be had by doing a good job for all that hardware out there.