I don't think those buttons work. But you can do it in code.
var is_full_screen = false
func _input(event):
if event.is_action_pressed("fullscreen"):
is_full_screen = !is_full_screen
if is_full_screen:
DisplayServer.window_set_mode(DisplayServer.WINDOW_MODE_FULLSCREEN)
else:
DisplayServer.window_set_mode(DisplayServer.WINDOW_MODE_WINDOWED)
DisplayServer.window_set_flag(DisplayServer.WINDOW_FLAG_BORDERLESS, false)
DisplayServer.window_set_size(Vector2i(1920, 1080))