EDIT: solved already, it was a windows update
I've been getting a very low framerate recently while playing but strangely, the fps becomes fine when I open the Windows startup menu or have another program on top as long as I'm not clicking on anything ingame. See video below.
I've already tried disabling Vsync and turning on triple buffering but it still acts like this.
Not sure how exactly it happened, but it's been acting like this since I left it open while playing VR, though the previous times I've done that didn't do anything.