How can I bind "modifier + arrow" keys to home/end/pageup/pagedown under X?

I have a new 60% keyboard (NuPhy Air60), but it does not have any way to trigger pageup/pagedown or home/end keys. My goal is to recover these commands with a custom keybinding, using a modifier key like hyper or alt, in combination with the arrow keys. For my preference, something like: - alt + arrowup = pageup - alt + arrowdown = pagedown - alt + arrowleft = home - alt + arrowright = end I tried to use xmodmap to make the bindings -- but unfortunately due to a years-old known chromium bug, my bindings there did not work in Chrome or VSCode. What else can be done?