Clean Windows 10 install, Ctrl+Backspace not working anywhere
Solution 1:
I solved it. Just as soon as I posted the most recent edit, I remembered that I plugged the keyboard into a USB port tagged with HOTKEY, which is a special port which allows me to boot my computer via my keyboard and some other silly things.
Just to see if that could possibly have anything to do with it, I put my keyboard into another USB and that solved the issue. I then looked at my motherboard's manual (its an MSI Z170a M7) and for some absurd reason they set Ctrl+Backspace as the shortcut for their "HOTKEY function" which does some more silly things. Why they didn't choose literally any other combination, I have no idea. But, well, that solves it. Now I just need to find out if I can change the combination for that HOTKEY function or if I'll simply need to keep my keyboard in another USB port.
But that's a different matter.