Update 14-05-2022: Dominaria United will lead into the Brothers War, followed up by 2 more sets featuring (what I assume) the war against the Phyrexians.
08-04-2022: Some art by Leon Tucker from the upcoming Magic: The Gathering set called The Brothers War have been leaked! The images have Factory in their filenames, and seem to be depicting Urza walking through a giant Mech factory.
Then there is this spoiler image posted by Wizards themselves!
Magic’s final set of 2022 tells the pivotal story of two siblings who shaped the multiverse… We’re going back in time to give a first person look at the epic mech battle between brothers Urza and Mishra in The Brothers’ War. pic.twitter.com/3EO1p90HzV
— Magic: The Gathering (@wizards_magic) August 24, 2021