As we learned from the Infinity Saga, the major villain doesn't need to be introduced right away, nor do they need to be in each and every offering.

Source: https://collider.com/mcu-thanos-kang-the-conqueror/

The Infinity Saga Doctor Strange Sling Ring replica is the greatest example of a screen-accurate and detailed cosplay item above all.

Source: https://gamerant.com/how-to-cosplay-your-favorite-marvel-characters-a-shopping-guide/

The MCU has introduced quite a few alien races like the Kree and the Skrull across the Infinity Saga.

Source: https://www.cbr.com/strongest-marvel-characters-not-in-mcu/

The original Avengers, while a key part in the development of the MCU, are now either dead, retired, or focused on other activities, and the scenes shown in the intro and logo are part of the Infinity Saga.

Source: https://screenrant.com/secret-invasion-new-marvel-logo-changes/

Though much of the action doesn’t happen until the film’s explosive third act, shows the Avengers battling their sorrow over their greatest failure and battling history itself to save the universe in an emotionally fitting finale for the Infinity Saga.

Source: https://www.digitaltrends.com/movies/the-best-mcu-sequels-ranked/