Knocking feature on Live widget allows you to have restricted Live rooms where unexpected guests will not be able to participate. This feature is useful for example when having private meetings, coaching sessions or restricted breakout rooms.
You can allow this feature by clicking the "..." on the up-right corner of a live widget > click edit > check Knocking under Meeting options > Save.
You can see who is knocking by clicking People on the Live widget. You can either let the participant in or respond to them with a message.