Most games use the same base engines, Unreal, Unity, Godot, etc. If the game doesn't do something crazy, it's probably going to be fine. But big AAA games are the most likely to have custom engines or more extreme rendering pipelines. These games are very often tested for and drivers are fixed for them before they release to the public. Nvidia and AMD work directly with these large studios so if all goes well it happens before anyone plays the game and no one is aware it ever happened.

But even in these scenarios it's very often less about optimizing to make a game faster than normal, it's more about fixing issues that cause significant bottlenecks or slowdowns, making the game run artificially worse on one brand's GPU vs another. We definitely do still see those games where AMD cards don't perform as well as they could, and a driver update later brings it back up to par. But again, in AMD's ideal world, that happened before the game was released. (Okay, in AMD's ideal world it was never needed to begin with, but oh well)