Ubisoft has yet to say anything official regarding Assassin's Creed 2020, aside from confirming a 2020 title is indeed in development, but the leaks continue to pour in. Many are likely nonsense, but at the very least, one insider has indicated an Assassin's Creed reveal is coming soon.
What this does mean is players should expect some leaks beforehand, as often is the case with the Assassin's Creed franchise. Typically, before gameplay details, it's names, character names, and more from merch found in retail stores (such as when many thought Bayek's name was Ba Yek). If this latest leak is indeed legitimate, it follows this pattern, as it is a novel associated with the next game.
While Assassin's Creed is predominantly a video game franchise, it has spawned several novels and comic book companions as well. Both Assassin's Creed Origins and Odyssey had associated novels, and thanks to Amazon Germany, it seems that Assassin's Creed 2020 does as well. Players can see its Amazon page below, complete with a release date of November 17, 2020, and tags such as Valhalla and Ragnarok that reiterate its viking themes.
Where this gets interesting is that both Assassin's Creed Origins and Odyssey's related novels came out relatively close to the game. Assassin's Creed Origins released on October, 27, 2017, while its companion novel, Desert Oath, came out on October 10, 2017. Assassin's Creed Odyssey released on October 5, 2018, with Odyssey (The Official Novelization) following it on October 30, 2018.
In short, the novels came out within about 3-4 weeks of its associated book. This would suggest that Assassin's Creed 2020's release date would fall within that same time span, but on top of that, it's unlikely that it would be much later than that. Potential delays as a result of the coronavirus aside, December doesn't seem likely. November's a possibility for the franchise, as it has released during in the past, and would be likely if it were to fall on the same date as the Xbox Series X or PS5 release date (making it a next-gen launch title).
On the other hand, if it were to be a cross-gen title like Assassin's Creed Black Flag, then an October release date is as likely, given the time frame suggested by this novel and the release dates of the past two games. This should be taken all with a grain of salt, of course, and perhaps especially because of the tumultuous times; nonetheless, it seems that the next Assassin's Creed game is still set for 2020.
Assassin's Creed 2020 is in development.