you can use FSR on Nvidia too but you can't use DLSS on AMD. Nvidia has been trying so hard to force a monopoly for decades now with these features they lock down to not only their hardware but specific series of them.
it's reminiscent of Microsoft making sure Linux can't use a wide range of software via directx and such, forcing people to resort to WINE and effectively becoming an operating system monopoly outside of apples gated garden
meanwhile AMD let's everyone use their software tech and people cry foul the moment they do 1/1000th of the anti competitive behavior Nvidia does in its sleep, I mean this is literally just sponsoring a game