The things I would do with your system, in this order, is:
01 - Get the latest motherboard BIOS and the latest drivers for you motherboard on-board devices like audio, USB stuff, LAN stuff, etc. You can get this from the MB website.
02 - Turn off any CPU or Memory overclocking in the BIOS.
03 - Use “Display Driver Uninstaller” to clean out all remnants of the display driver then install the latest Nvidia driver.
04 - Make sure windows is completely updated and also check for updates in the Microsoft Store app.
If that don’t help, Re-Install windows then MSFS after you get windows updated.
One last thing, you mention you have a 650 Watt PSU. PSU’s can sometimes fail slowly and may not be supplying enough power to the GPU or CPU and this will be apparent under a load, such as gaming. I do not know of an easy way to check that. I just swap out to a known working PSU and see if that fixes things.
Good luck.