I can’t say what other people’s experiences are or what their problems stem from or how they can fix them.
But in my case this is repeatable. I’ve gone through this FOUR times. Every time I update my drivers in the geforce experience I get 10fps. When I do a “clean” install from downloaded drivers I go back to normal fps. I’m not saying the geforce experience is causing the issue inherently for sure. I was thinking it might simply be a clean install vs express install. But I did test a clean install from geforce experience and it did seems to fix the 10fps for one MSFS session. But next time I started MSFS it was back to 10fps. Installed clean from a file and it’s back to normal fps and has stayed that way for several MSFS sessions and at least one reboot. I am not saying this will fix everyone’s serious performance issues, but if someone can’t find a solution, this is certainly one I’d recommend people try.