Not sure if this is serious or in jest, but just in case, sidestory vs apocrypha is not at all a value judgement, it's just a matter of 'do I have future plans for this character and, if yes, could canonizing this get in the way'. So 'outside view' omakes from invented characters reacting to the events of the story very easily become Sidestory, as do peripheral worldbuilding like fictional books and whatnot, but an ambitious multi-chapter PoV from a canonical character is almost certain to end up in apocrypha just so they're free to go as nuts as they want with the character without worrying about stepping on canonical toes.