What you’re talking about might be “Synchronous Spacewarp” in Virtual Desktop, essentially when your PC can’t push enough FPS for your selected refresh rate it will lock at half of the refresh rate on your PC (45hz being half of 90) and estimate the rest of the frames using the chip on the headset itself.
You can try turning that off under the streaming section inside Virtual Desktop on your headset and see if you notice a difference, it won’t make your FPS any higher but you should be able to see your FPS vary a little more and a difference in smoothness (usually worse when off).