FSR 1 isn't that great. It's basically a well-known upscaling algorithm (Lanczos), tweaked for edge detection and with a sharpening filter. It's super lightweight, but definitely doesn't provide "near native" quality by any stretch. FSR 2 significantly altered the algorithm and looks better, but with a higher performance impact. It still can't match DLSS 2 upscaling in overall quality, though at times it's at least close, particularly in quality mode when targeting 4K.
I believe Unreal Engine is working on its own internal temporal upscaling solution. It would basically be like FSR 2 in that it would work on any GPU, leveraging the GPU compute shaders to do the computations. I'd be super impressed if Epic took the extra step of having the algorithm leverage tensor / matrix hardware if available, but I seriously doubt that will happen. Whether it will look as good as FSR 2, or better, remains an open question.