At first i was also in the assumption that virtual desktop only would work with the steamvariant of the game. But after changing the openxr path to steam (like twisted mentioned) it worked.
You can change it in the properties of steamvr in your steam account.
After that you start up steam vr and virtual desktop. Then you start the game from virtual desktop the same way you would on your flat screen. Then hit ctrl-tab and the game goes into vr mode once youre in your plane.
Edit:
You dont have to use the oculus software at all btw!