Here’s a thread that might point you in a good direction.
Poor ground performance is caused by an overworked CPU rather than the GPU.
There are a few graphical options that tax the CPU, and most of us aren’t used to graphics settings taxing the CPU rather than the GPU.
This is especially problematic on PC’s with limited CPU clock speed like laptops which would get too hot if they run any faster than they do.
Your Terrain LOD setting is the first thing to adjust if you want smooth ground performance.
This is the most common issue with MSFS and it stems from people fundamentally misunderstanding what all the graphical sliders are meant to do.