Just for good measure, I tried with Pimax Crystal, and no issue here too 
So I suspect you have a bad combo with something else interfering.
Note that with the way MSFS implements foveated rendering, it’s pretty transparent to the platform/OpenXR (especially now that the eye tracking isn’t queried). The engine submits stereo, which is pretty much the same thing with/without foveated rendering.
I tested this combo btw:
- Pimax Crystal (not Light)
- Pimax Client 1.38.02.01
- PimaxXR (not Pimax Play) 0.4.4
- No API layers of any kind
- No mods to the game of any kind (no DLSS dll swap etc)
- No 3rd party “performance” tools of any kind (Riva tuner & co)
- All defaults in NVCP
- Nvidia driver 572.70 (that’s one version behind)