It appears one of Ubisoft's announcements for its Ubisoft Forward event at E3 2021 today has leaked ahead of time. Nintendo's own website has been updated with a listing for the unannounced game Mario + Rabbids Sparks of Hope for Nintendo Switch.
The sequel is coming in 2022 with characters like Mario, Luigi, Princess Peach, Rabbid Peach, Rabbid Luigi, and more. They're on a "galactic journey to defeat a malevolent entity and save your Spark companions." The game's description adds: "Explore planets throughout the galaxy as you uncover mysterious secrets and compelling quests!"