First, I start AFS2 (latest beta) in Steam, then select Steam VR mode when prompted.
When I set graphic driver to Vulkan, my WMR Headset just displays the "grey room" I used to see before getting AFS2 home menu. The 6dof tracking remains ok, and everything on my 22-inches monitor seems to be ok, except for the yoke and the quadrant that are not responding (display, sound, keyboard and mouse ok).
Reverting to OpenGL causes normal display in the headset. Restarting AFS2 (Steam VR mode) causes everything working back again.
Hope this could help to debug.