Hi,
I use a Quest 2 headset, not Pimax sorry. But I can relate to the experience you outlined regarding high frame times and the red bar appearing.
Yes, I believe frames are being dropped because it takes longer for your PC to generate the frames than what the headset can display (in other words, by the time the frame has finished being created, a new one is already required). I’d imagine you may also be experiencing stutters as a result?
Are you currently running the maximum FOV (e.g., 200deg) with your headset?
As a temporary measure, what happens if you cap your max FPS in nvidia control panel to 45, lower your VR resolution, and lower your OLD and TLOD to 75 (for both) in the sim?
If these temporary adjustments improves your performance, you should be able to maintain solid green bars in the MSFS FPS counter and stutters should disappear. Ideally, you want to try and retain solid green all the time, with only occasional flickers of yellow.
If that all works, then try increasing each setting one at a time to see what impacts the frame times the most.
Hope some of this might be useful to you, apologies if you’ve already tried some or all of it. Let me know how you get on.
Cheers,