The Promised Neverland Ending, Explained
The anime and the manga end differently, and the difference is a price. In one of them Emma pays it, and in the other the show simply stops charging.
Spoilers throughout. This page assumes you have finished the series.
Two endings, and unusually for this site the gap between them is not a matter of taste. One of them removes the thing the story was about.
What the manga does
Emma makes a bargain with the demon god, the entity called The One. In exchange for safe passage to the human world for her whole family, she gives up her memories of them. The escape succeeds. Two years later they find her again, and she does not know who they are.
That is a hard ending, and it is the ending the series was built for. The Promised Neverland runs on the idea that getting out costs something, that the children are trading away pieces of themselves at every stage, and the final trade is the largest version of a bargain the story has been making since the first episode.
What the anime does
Season 2 compressed roughly chapters 38 to 181 into six episodes. It cut the Goldy Pond arc entirely, skipped or rewrote several others, and arrived at the finale without most of the material the ending was supposed to land on.
So the bargain does not happen. The One appears briefly in a closing montage rather than as a party to a deal, Emma pays nothing, and everyone is reunited. The children get out, and the escape is free.
Why that breaks it
Removing the cost does not simply shorten the story, it contradicts it. A thriller about children escaping a farm where they are livestock is powered by the sense that the world charges for everything, and the finale answers the question the whole series was asking with "nothing, actually". The plot arrives at the same physical location as the manga and means the opposite thing on arrival.
It is worth being fair about one thing: the manga's own ending is divisive, and plenty of readers find the memory bargain contrived. The complaint about the anime is not that it departed from a perfect original. It is that it kept the destination and deleted the fare.
How this compares to a good divergence
Fullmetal Alchemist's 2003 anime also ran ahead of its manga and invented a conclusion, and it produced something coherent and deliberate that argues with the source on purpose. That is the case for adaptations diverging. The Promised Neverland's second season is the case against doing it in six episodes.