This was a USA thing last week when it was sold but still widely in stock in the UK. That has changed. The Pro is sold out at many retailers in the UK. GTA6 hype is real.
I bought a Pro 2 months ago for the game but haven't watched extended gameplay the base console will be fine. 60FPS won't happen to justify the Pro. Pro will just have better lighting and detail and possibly fewer frame drops during busy scenes.
If the benefits is tiny I might even end up selling my pro for a profit and replacing it with the base. I will only be using the console to play that game.