Ubisoft has been staying away Steam since some time, and the reason behind this was the business model used by Valve. Finally they are bringing some of their games back to the platform, starting with Assassin’s Creed Valhalla just on the day its final content update.
There are some other Ubisoft games coming back such as Anno 1800 and Roller Champions. Their spokesperson said that the company is both evaluating how they could present their games to different audiences and provide a constant player ecosystem through Ubisoft Connect.
It was in 2019 that Ubisoft separated itself from Steam. There were some serious titles such as Ghost Recon Breakpoint, The Division 2 and Assassin’s Creed Valhalla, not coming to Steam but released via Epic Games Store besides their own platform. Epic Games Store is known to provide a more generous share to developers, so Ubisoft made its choice in favor of Epic Games Store.
Currently there is no information whether Ubisoft will bring all games or not.