I've recently discovered FLTK: https://www.fltk.org/doc-1.4/intro.html

Haven't used Qt in a while, but at first glance, seems simpler: https://github.com/fltk/fltk/blob/master/examples/menubar-ad...

Yeah for my work, legacy Win32/WinForms/WPF codebases tools are kept maintained as-is, but new tools are usually written in PySide6 (QtWidgets or QtQuick) and it's worked out really well (other than bundling/distribution being tricky for big apps)

MFC is rock solid too

And Lazarus/FPC.