@Tourmaline, this is the Windows forum.
I'm not sure what is "Change to previously selected input", under Windows, but I'm quite sure that the only reserved keys include Win key, not Ctrl (ok, Ctrl-Alt-Del ;)).
1. If you try Windows, you'll notice that Ctl+, Alt+, Shift+, Win+ hotkeys always start with the special key (Ctrl, Alt, Space, Shift, Win). It's a simple UI standard. It's something your fingers learn how to do, not your brain.
2. If you try any of the Adobe products, you'll notice that Ctrl+Space is the key to invoke Zoom tool. (Space+Ctrl also works). So if it's possible for Adobe it will be more than possible for Serif ;). And as much as I like Affinity products, the standard was set by Adobe 30 years ago.
Serif's Affinity Designer is a great program, which I use daily, and has already convinced more people to switch to from Illustrator.
Serif, let's beat the competition once more!