He complained there is no way to do the easy thing in Wayland - there is a way: Gtk and QT

How do you make a global hotkey in all compositors with Gtk or Qt?

...which is overkill when you only need a Vulkan or GL canvas which spans the windows client area... and even with GTK or Qt your app still stands out like a sore thumb on the "other" desktop environment because the window chrome doesn't match the rest of the system.