The CPU improvement on the PS5 Pro, at least from the leaks so far, is not much of an upgrade. A game of this size will be very taxing on the CPU, akin to Dragon's Dogma 2 where there's so much continuous backgrounded processes happening in real time that the GPU wouldn't be handling since it wouldn't be displaying them yet.
I trust Rockstar to optimize the game a lot more than Dragon's Dogma 2, but I think it will be a solid 30fps at best.