You can animate the alpha-value of their modulate
-property. For example you could add a Tween-node as a child of your Label / Button / Sprite with this script:
extends Tween
func fade_out(duration := 1.0):
interpolate_property(get_parent(),"modulate:a", null, 0.0, duration)
start()
yield(self, "tween_all_completed")
get_parent().hide()
Than all you have to do is get the Tween-node and call the fade_out
-method.