Is the joke in Joker a joke on those who think it is real?

Rating: 2/10 (20 March 2020)

All through, I wondered just how this incompetent inadequate man could suddenly become a criminal mastermind.
A random murderer, yes. You just need a gun and to choose targets who don't suppose anyone would be crazy enough to kill them.
But how can be transform into Batman's worst foe?
Given some games with what's real and what's not, I wondered if perhaps the film is actually saying none of it really happened. All the fantasy of a man in a mental asylum. (Which has been done, or similar, in other films.)
Which would make it a nice spoof for all those who've been delighted by it. You have been mocked and don't yet realise it.