Why can't I select an object in matinee?

So I’m attempting to create a veeery simple matinee to animate a door opening - I am a complete noob. In very single tutorial I have seen, they select the actor, then move over into the matinee and add in a keyframe. I have successfully created a matinee using only a camera before, but whenever I select an object and then attempt to create a movement channel, the object de-selects. This is infuriating. Can anyone help?