GtkWindowunmaximize

Asks to unmaximize the window.

Note that you shouldn’t assume the window is definitely unmaximized afterward, because other entities (e.g. the user or window manager) maximize it again, and not all window managers honor requests to unmaximize.

You can track the result of this operation via the GdkToplevel:state property, or by listening to notifications on the GtkWindow:maximized property.