So it seems Joker being involved in the story is a new development rather than something that had been planned years earlier.
The upcoming HBO Max event, informally known as The Snyder Cut, is currently in the midst of shooting new footage, and THR has heard that Jared Leto is involved with this.
What’s interesting about this is that not only was Jared Leto’s Joker nowhere to be seen in the theatrical version of Justice League, but there was never any word about him appearing in Zack Snyder’s version of the movie.