I’m not sure how recently you installed windows fresh or if it’s an option and install nothing but msfs. I recently found my constant stutters on my 7800x3d were caused by the first thing I install after windows 11 which was MSI afterburner. When set to monitor things like GPU power, it somehow causes stutters every time it polls the gpu. I had set it to poll every 100ms so you can imagine what a stutter every 100ms looks like not good.
Just thinking as a last resort you could possibly reinstall windows just to see can even a super clean windows install help and retest after each piece of software you install after that to see what might be the culprit if it is a software and not hardware or uefi setting as the culprit.