What is the best way to design GUI on ARM cortex-M microcontrollers?
According to this post from two years ago, it is not possible to run QT framework without an OS.

If emWin is too ugly for you, you may be able to write your own widgets for it, beautifying it more, or you could roll your own which I imagine is popular with people who are picky about look-and-feel at this level of hardware.