I don’t have any payware scenery for MSFS 2020, but I can say that at the freeware Gatwick 2024 on Flightsim.to I get around 30-35 fps in the FBW a320nx and unfortunately with vatsim 25-30fps (In typical cloudy British weather)!
Thanks
PS - I have 16gb of RAM but would upgrading it to 32gb help? (I’m new to the world of PC’s)