If you are buying a Pro for 60 fps in GTA 6, wait for launch. Rockstar committed to 30 fps on consoles and has announced no Pro mode. The PS5 Pro Enhanced label on the PlayStation Store means the game has Pro-specific settings, and neither Rockstar nor Sony has said what they are. Digital Foundry calls 60 fps on the Pro extremely unlikely: the Pro's CPU is only about 7 % faster than the base PS5's, which is not enough to double the frame rate. Digital Foundry expects the extra GPU power to go into PSSR reconstruction, better ray-traced lighting and less shimmering on fine detail, which the trailer footage showed on the base console.
Some players hope for a 40 fps mode on 120 Hz screens. Nobody has reported one. We will list the real modes on the performance page once the settings menu is documented.