I too was having these issues, lower fps at/over airports, studders in high gen areas (NYC/LAX/CDG/LHR, etc. I followed a msfs performance tips guide which directed me to change the windows page sys file to equal the amount of ram I have (32GB-3733MHZ)-CPU/3800X GPU/5700XT sim on M2 drive.
I run at 2880x1440p at high settings with clouds on Ultra. A few settings relating to the drone camera off as I don’t use it. When I now fly over those same areas I start at the runway let it settle for about 20 secs. FPS 30-35 with clouds in the sky. Very Important - turn of the VFR map in the settings when in the cockpit, you will gain more fps and the studders for me went away. When I fly over say NYC my fps are around 30-35 but sometimes dips in the high 20’s for a few secs. Other thing I did was on the MSfightsimulator.exe, I checked Disable full screen opt. and override high dpi settings. Those things has helped me alot. I hope the next update will increase performance or move the sim forward. Sim runs pretty good right now.