Returns whether surfaces on this this are created with an alpha channel.
Even if a true is returned, it is possible that the surface’s alpha channel won’t be honored when displaying the surface on the screen: in particular, for X an appropriate windowing manager and compositing manager must be running to provide appropriate display. Use [method@Gdk.Display.is_composited] to check if that is the case.
On modern displays, this value is always true.
true if surfaces are created with an alpha channel or false if the display does not support this functionality.