One unusual alternative you may not have thought about is using Godot Game Engine. Before dismissing it, consider this: Godot engine is shockingly small for what it does. The download is about 30-40 MB. The GUI designer tool is second to none, and you can make highly interactive advanced GUIs using a language that looks very much like Python called GDScript. It is very quick to learn.

It does make GUI which are native to the platform but you get a small native binary which renders OpenGL.

Is Making Advanced GUI Applications with Godot the Future? https://medium.com/swlh/what-makes-godot-engine-great-for-ad...