When I saw the submodule /ETEngine/Engine/third_party/gtk/GTK-for-Windows-Runtime-Environment-Installer I immediately know your project doesn't support MSYS2 MINGW64. Because on MSYS2 MINGW64, this submodule is absolutely not needed as we have packages for GTK3 and GTK-for-Windows-Runtime-Environment-Installer is indeed made using MSYS2's GTK3 packages.
When I saw the submodule
/ETEngine/Engine/third_party/gtk/GTK-for-Windows-Runtime-Environment-InstallerI immediately know your project doesn't support MSYS2 MINGW64. Because on MSYS2 MINGW64, this submodule is absolutely not needed as we have packages for GTK3 andGTK-for-Windows-Runtime-Environment-Installeris indeed made using MSYS2's GTK3 packages.