Pretty much any non-web GUI framework I tried so far has either been terrible to set up, or terrible to deploy. Or both. Electron is stupidly simple.

ImGUI is the single exception that has been simple to set up, trivial to deploy (there is nothing to deploy, including it is all that's needed), and nice to use.

Tkinter is easy too.

Except ImGUI’s missing what I consider essential features for macOS: proper multitouch support (two finger panning, pinch to zoom).

Specifically for panning and zooming, doesn't the OS translate those inputs to mouse events, like Windows does by default? Otherwise it is simply a matter of performing this translation at the backend level.