I use this guide to optimise my settings.
It also helps me to disable Hardware Virtualisation Technology and VT-d in my motherboard BIOS. It helps to stop the virtualisation function in the CPU and allows MSFS to take full utilisation of the CPU, removing the stutters as well as getting a stable frame rate at higher settings.
Disabling this changed my FPS from running in the 10-15 fps on Low settings and limited by mainthread, to a stable 30 fps on ULTRA at 2160p, that switches into limited by GPU, which is better.