openXR resolution is for everything outside of the cockpit. The renderscale in game is for everything inside the cockpit.
So if you like nice visuals of the buildings and the world, you should try openXR at 100.
If you want to read the instruments inside the cockpit, you should set the ingame renderscale at 100.
Sadly, every system is different. There is no golden rule for this settings. Just try and see what works the best for you.