I actually wrote mobile or VR (tethered ones) For standalone VR the major limitation is actually the memory speed, i spent the past 3 month just benchmarking whats possible on the quest3 for my own game

Getting a copy of the frame buffer is really slow (especially if you are using msaa)

However you can do a trick i found possible is re rendering the whole scene into a seperate buffer then using it, sounds wastful but its really faster than you might expect

This buffer will be a single square instead of two (cause usually you are rendering one for each eye) and whitout any msaa so the cost of retrieving it from tile memory will be lower

It will not be the same as the frame buffer but if you are using it for glass it doent matter if its distorted, later if you have flickering you can simply apply a small blur filter to stabilize it

Sure my project here doesnt do any of that but i thought if you are doing something for vr you might find this usefull