An alternative in C++ would be wxWidgets which has some (light) MFC inspirations, again feeling somewhat Windowsy though not full-on MFC/Win32 since from the beginning it had to work with X Windows / Motif in addition to Win32 (and AFAIK, the Motif backend still works).
Another alternative, even more lightweight would be the aforementioned FLTK. FLTK is also designed to be statically linked with your program (though it can be linked dynamically too if you want) so it only relies on common system libraries (as an example the screenshot in [0] relies only on the C library, the C++ library -because it is needed by FLTK and it is possible to also statically link to that too- and common X11 libraries like libX11, libXft, etc that existed on any Linux desktop system for decades now -- FLTK can also support Wayland, though i haven't tested that).