what do you mean... MM performance mode is the PS4 Pro version but at 60fps
they LATER added a performance RT mode, obviously PS4 cant do RT. sine this game doesnt have RT i fully expect PS4 Pro version at 60fps
I think it'll be somewhere in between the 30 Hz mode on PS5 and the 30 Hz mode on PS4 Pro.
They may just drop res from say 4K CB to native 1440p, and then just disable certain visual effects they use in the 30 Hz mode. They said the PS5 version has its own water tech, better than on PS4. I bet some of these things will be on PS5 even at 60. They also said that the extra hero lighting on Aloy is only used in cutscenes on PS4, but they can have on all the time on PS5 in gameplay (at 30 Hz I assume.) That type of stuff will likely get turned off for the 60 mode. Even if graphically its similar to PS4 Pro, it'll still be 60 FPS and have better audio, DualSense support, and very fast loading. Not bad.
Also, Guerrilla say the PS5 version uses ray tracing for rendering, physics, and audio. So it does have the GPU's RT cores in use.