Since 2.9 patch dropped, openXR motion controller mapping is finally fixed, on HP reverb G2, the trigger, palm grip and trackpads (I use WMR controllers so I have trackpads) all work. finally.
(See my original post where it wasn't working before
The only problem now is: menu buttons are not mapped. pressing menu button is not recognized in game.
At least the patch keeps progressing, I hope it eventually fix all the problems.