In preparing for Avengers: Secret Wars, the MCU still needs to introduce several villains, so it can effectively stick the landing. The MCU took its biggest leap yet into truly establishing the Multiverse Saga by introducing the presumptive big bad, Kang the Conqueror, in Ant-Man and the Wasp: Quantumania. The ongoing in Phases 5 and 6 will all culminate in the collapse of the multiverse from incursions and, likely, in the formation of the Battleworld. Yet, the MCU still has a great deal of groundwork to lay before then if they’re going to follow the various Secret Wars comic series as written by Jim Shooter and later Jonathan Hickman.
https://screenrant.com/avengers-6-secret-wars-villain-missing-mcu-fix/