NetherRealm Studios has established a pattern of alternating between Mortal Kombat and Injustice games since the studio started in 2011. Considering this, many fans assume that Injustice 3 will be the studio's next game, though nothing official has been announced. This assumption has also fueled supposed "leaks" online, and there's one that's making the rounds that's almost certainly fake.
A new rumor being spread online claims to reveal specific details about Injustice 3. The "leaker" claims that they work for an international branch of WB Games. They claim that the game is set to launch in May 2021, with Joaquin Phoenix potentially being used for The Joker's likeness. Robert Pattinson's Batman will also be available for Injustice 3 as a pre-order bonus, and Neo from The Matrix will be a day one DLC character to tie-in to The Matrix 4 movie. Keanu Reeves has supposedly signed a deal to voice Neo in the game, and more Matrix content will be found via Trinity cosmetics for Catwoman.
The leaker goes on to say that Injustice 3 will have two story modes, one that continues the story of the first two games and the other that focuses on an alternate timeline Justice League. The game will apparently have a big focus on cosmetics and customization, with the example being that it's possible to make The Joker a Red Lantern Corps member. They also claim that the game will feature Huntress and Penguin as new characters, with Hawkgirl and Lex Luthor returning from the first game after they were absent from Injustice 2.
There are a couple of big reasons why fans should disregard this particular Injustice 3 rumor. For one, while Injustice 3 could very well be in development, it's highly unlikely that things like a Keanu Reeves voice acting deal or Joaquin Phoenix Joker rights would be nailed down at this stage. And secondly, another poster on the Reddit thread where this leak originated stated that they checked with someone who would know if this was real, and they said it was fake, also accusing the original poster of lying about working for WB Games. The Reddit thread has since been deleted, so it's possible that concrete evidence was provided to the mods that proved the leak was fake.
Even so, this hasn't stopped the Injustice 3 rumor from spreading online, showing that fans are excited to learn more about the game, whenever it does materialize. For now, though, NetherRealm is still busy working on Mortal Kombat 11, having yet to release the Spawn DLC character and possibly even prepping Kombat Pack 2. Considering this, it may be quite a long time before fans see Injustice 3 or whatever project NetherRealm will release next.
Injustice 3 is rumored to be in development for next-gen consoles.