I've been testing this extensively the past several days to figure out exactly what causes this. As others have experienced, I have the same stuttering issue in and out of menus with a Ryzen CPU when frame gen is enabled. It has nothing to do with your display. The issue is triggered by how much load is on your GPU when you go into or out of menus and/or cutscenes. If you have frame gen enabled and your GPU is at or very near full load when you go into the map/inventory/settings screens, then you will get severe stuttering when you close those screens and go back into the game. However, if you configure your game settings in such a way where the GPU stays under full load at all times, the stuttering is largely eliminated. Not completely eliminated mind you, but it's mostly gone except for maybe a tiny hiccup coming out of the menu screens here and there.
There seems to be some kind of problem in this game with the way the GPU and Ryzen CPU's keep step with the game engine (and each other) when the GPU is at full load with frame gen enabled. In these instances, it seems like the game engine is massively spiking the load to the GPU temporarily beyond its limits and the GPU has to take several seconds to catch up. I've managed to produce a manually-repeatable crash from this by going into and out of the menu screens rapidly with GPU at 100% load and frame gen enabled. The Windows crash report points to the GPU driver not being able to keep up with the requests being made by the game.
In short, when it comes to the stuttering issue, the game settings and display don't matter, what matters is the GPU load percentage when frame gen is on. If you have a Ryzen CPU, try to keep GPU load at or under 90% at all times. Hopefully this annoying issue gets fixed at some point as it's been going on since frame gen came out.