Using my fresh install of Qubes 4.1.2 I found myself somehow (clearly a result of careless mashing at the keyboard) stuck in an obnoxious screen magnification conundrum. If this sounds like you, try holding down the Alt key and scrolling. If you're on a laptop that does not have designated scroll bars on its (multitouch) touchpad the default XFCE emulation for a scrollwheel is two-fingered scrolling. Now instead of a nuisance we have discovered a handy tool together!