I think it’s safe to say that MSFS is currently very picky when using VR. Turning on Mixed Reality after MSFS started usually leads to crashes. Starting MSFS from inside Mixed Reality Portal leads to audio or video (or both) missing or crashes. Having Steam open leads to crashes sometimes as well even though SteamVR isn’t running. There is still a way to go to make MSFS a proper Mixed Reality application.
All experiences based on HP Reverb G2 v2 usage.