First flight with new version of Mixed Reality Runtime 112.2209.200. Here MR also works better than before.
I do not need to ALT-Tab out to get good performance! Only when switching out of VR and back in, i get stuttering and can solve it only by CTRL-ALT-DEL/ESC. But this could also be an MSFS problem.
Many thanks OpenXR-Team, keep up the good work!
Edit: Win10, 5800X/32GB, 3070ti