Most interpretations I've found online, including a few on this site, seem to believe that the events of Joker are all imagined, and the only "real" scene is the final scene, with Joker in Arkham Asylum.
If this is the case, can someone explain why, when the camera pans past the face of the social worker who is questioning him in the final scene, we see Arthur standing in the shadows behind her? It's like he's an observer, which makes the scene feel like it's imagined as well. Am I missing something?