cx_Freeze has hard-coded
libffi-7.dll in the source: add ctypes hook in Python 3.8 for windows.
But at present, MSYS2 ships with
libffi-6.dll and so things break.
Filed bug upstream: fix version of hard-coded libffi DLL.
cx_Freeze ticket: libffi-7.dll not found with msys2/mingw64
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2611