Comment by codedokode

Gtk and Qt are not reactive. "reactive" means that you have a variable ("model") bound to the property of UI widget (for example, slider position) and every time you update the variable, the UI widget redraws itself automatically. UI widget property might be also bound to an expression containing multiple model variables. As far as I know, both Qt and GTK require you to update widget properties manually like in 80s.

Flutter is built on unpopular slow dynamic interpreted language that is used only by Google. My only experience with Dart is when Google Ad management site was built on Dart compiled into JS, and it loaded and worked very slowly compared to normal sites, used lot of RAM and I dislike Dart since then.