re, iteration: Have you encountered ImGui [0]? It's basically standard when prototyping any sort of graphical application.

re, GUIs in statically typed languages: As you might expect, folks typically use a library. See Unreal Engine, raylib, godot, qt, etc. Sans that, any sort of 2D graphics library can get the job done with a little work.

You might also take a look at SwiftUI if you have an Apple device.

[0]: https://github.com/ocornut/imgui