What defines a film as part of the mcu multiverse?

The Marvel Cinematic Universe’s multiverse is defined as a setting that includes infinitely many alternate realities and dimensions. It first appears in the 2016 film Doctor Strange, where the concept of multiple planes of existence is introduced, and is revisited in Avengers: Endgame (2019) as a branching of timelines. The multiverse becomes a central theme in Phases Four, Five, and Six, collectively known as The Multiverse Saga. In these stories, the MCU’s multiverse centers on a universe sometimes referred to as the "Sacred Timeline," a bundle of closely aligned, infinite timelines that do not lead to the emergence of a Kang variant. The Time Variance Authority (TVA) initially pruned branched timelines, but the narrative shift occurs when Sylvie kills the TVA’s leader, "He Who Remains," allowing other timelines to persist. Therefore, a film is deemed part of the MCU multiverse if it portrays or references these alternate realities, involves the Sacred Timeline, and belongs to the phases that explore multiversal themes.