In my opinion, the best GUI approach is still JUCE. Every UI element is a C++ class with a drawing function. You create new UI elements by composing other elements to create another C++ class, for which the editor will auto-generate the source code. For buttons, you have a large if...else... area in the drawing function to handle different states like hover, pressed, active, disabled, etc. Behind the scenes, a thin drawing library will use Metal/OpenGL/DirectX as needed.

I find it refreshing that everything is imperative. You can put a breakpoint anywhere and you'll see when it gets called, with which parameters, by whom. You can also export intermediate rendering states to imdraw. Plus it's almost pixel-perfect (except for font antialiasing) on all platforms.

The XML variant being peddled here is, in my opinion, exactly what I usually try to avoid: framework-dependent magic. I'm 100% sure that 3 framework upgrades down the line, the layout will be slightly off. Because it was never you owning the layout, it was always you begging the framework for its consideration. The only thing that somewhat mitigates this issue with Electron is that it uses "old" technology. CSS isn't going to change much by itself anymore.