As revealed by the departure of an employee, Blizzard has apparently been working on a new game for at least two years, which we will not get to see. The development has been halted. This is stated by an animator who previously worked on Overwatch.
Where does the information come from? The information comes from animator David Gibson. It can be found in his resume on LinkedIn and from some statements on Twitter after his departure.
Gibson worked for Blizzard from March 2015 to August 2017 on Overwatch. There, he brought Mei to life and made sure that opening loot boxes in Overwatch is spectacular or contributed to the events that followed the launch of Overwatch.
From June 2017 until the last days, Gibson then switched to a “yet-to-be-announced project”. He does not reveal the name of the project.

This information comes from his LinkedIn page.
This is what Gibson says: On Twitter, Gibson announces his departure from Blizzard. He says they worked on something for the last two years that no one will ever see. That’s just how game development works.
But players have Overwatch for that.
Details on what the game was or was supposed to be, Gibson does not reveal.
In a conversation with a colleague, he says it was great to be hired to make a significant game about robots and girls, girls and robots. However, this description also fits with a bit of imagination on Overwatch, the game for which he was directly hired and which is known for its strong female characters.
Activision pushes for new games
This is what’s behind it: Generally, it’s not unusual for a game to be canceled while still in early development . At Blizzard, there was the well-known victim of the MMORPG Titan, into which a lot of time and money was invested and which did not come to fruition.
In the specific case of “Blizzard,” however, it is interesting because Activision apparently criticizes Blizzard in recent years for not releasing enough new games. Therefore, Activision is reportedly tightening the reins and urging Blizzard to better manage its resources.
Activision Blizzard has laid off 800 employees this year because apparently there are not enough games to support such a large publishing team.

What is Blizzard developing? Among the titles that are at least rumored to be in development at Blizzard are
Currently, only Diablo Immortal and Warcraft III Reforged have been officially announced.
Update: Meanwhile, it is known which game has been canceled. It was a “Starcraft shooter.”