Environment: Windows 10 Pro - Code :: Blocks version 20.03 - Msys2 with Gtk3.0. Other linker options: `pkg-config --libs gtk + -3.0`. Other compiler options: `pkg-config --cflags gtk + -3.0`. After several unsuccessful attempts, I uninstalled version 20.03 and installed 17.12, running without problems. Maybe a bug in version 20.03?