FSR 3 doesn’t have a system wide implementation. It’s in pipeline just like FSR 2. FSR 1 is the only version that can be applied at a system level, specifically because it’s an output filter, not part of the render pipeline.

There may be something in the Adrenaline software for AMD GPUs that allows applying some portion of FSR 3. I have an Nvidia card, so I can’t speak to that, but it would have to be using some form of injection, such as the Anti-Lag feature AMD tried to offer and then pulled, because it ended up getting people banned for triggering anticheat. That’s only possible at a driver level, though.