Libui works on multiple platforms with native UI. QT, GTK and Fyne work around this each in their own way. Fyne is a very interesting solution as it just renders everything in OpenGL.
At first I didn’t like Fyne but from a visual standpoint but after switching to the light theme it has really grown on me. And the cross platform bugs I used to get with libui are pretty much non existent. It is so much simpler to support one rendering engine that all of the platforms support vs multiple implementations of the same thing. It might work for simple apps but the platform specific quirks start adding up and it becomes a maintenance headache. After switching to Fyne I’ve been very happy.