If a QMainWindow contains a QOpenGLWidget, the macOS unified toolbar does not work anymore. It worked up to Qt 6.3.2, but starting at Qt 6.4 (and now Qt 6.5), the property unifiedTitleAndToolBarOnMac does not have the desired effect anymore. The two attached screenshots show the difference. Both show the official Qt 2D Painting Example , but with the statement "Window window;" in main.cpp replaced by

QMainWindow window;
window.addToolBar("ToolBar")->addAction(new QAction("Test"));
window.setUnifiedTitleAndToolBarOnMac(true);
window.setCentralWidget(new Window);

The Qt 6.5 version still has a separate title bar, while it is merged with the toolbar in the Qt 6.3 version.