FSR is AMD’s name for their software upscaling technology. I guess Sony went and wrote their own upscaler because as someone above pointed out PS5 technically already had FSR, but similar to Nvidia DLSS, it’s all the same idea : render a small frame image (like 720/1080) at higher quality detail and use AI to blow the frame up to 4k before it reaches the display.

https://www.amd.com/en/products/graphics/technologies/fidelityfx/super-resolution.html