Window.fullscreenOnMonitor

Asks to place window in the fullscreen state on the given monitor.

Note that you shouldn't assume the window is definitely fullscreen afterward, or that the windowing system allows fullscreen windows on any given monitor.

You can track the result of this operation via the [gdk.toplevel.Toplevel.state] property, or by listening to notifications of the [gtk.window.Window.fullscreened] property.