I am really unsure how to answer this question.
On the one hand, Writing a GUI Windows app using the Win32 API is actually not that hard. Each GUI development environment has a learning curve, and once a certain level of triviality is exceeded, they are all as equally easy, or hard, to master.
MFC is very little more than a C++ wrapper around the basic windows concepts. The windows API for example has a HWND - handle to a window, that you can pass to functions like ShowWindow().
MFC has a CWnd that encapsulates an HWND, and has methods, such as Show(). The problem with MFC's wrapping of the underlying API is, well CWnds have different lifespans to the handles they wrap, as well as different restrictions. CWnds are for example not particularly thread safe - whereas its completely safe to access an HWND from many threads (and processes) at the same time.
All that said, if you want a mature c++ development environment thats good for writing GUI apps that can run on MacOS, Windows and Ubuntu: Qt Creator might be worth a try. Its far more independent of the underlying native API than MFC, but I can confirm that projects written in the Qt framework (using Qt Creator) can just be rebuilt to run on MacOS just as easilly as Windows.