I looked to port Gtk to MCU, and then gave up. Too much C trickery, and hard to replace, heavy dependencirs.
For somebody who knew Qt, and Gtk since 2003, it looks like a miracle now how Qt got smaller, and faster than Gtk, and can even run on an MCU, and quite well!
Very big contribution to that was Qt's team willingness to undo the wheel reinvention, and willingness to throw out their hacky attempts to replicate new c++, and standard lib functionality.
The Glib+Gtk world, unlike Qt, still lives in ANSI C, and C99 era, and refuses to concede on reinventing functionality of modern standard libraries, language features, and compilers.