There are a number of adaptational changes that Denis Villeneuve's Dune movies make. I think the general consensus is that these changes are largely wise (I wish we'd gotten a bit more of the Spacing Guild, whose entire appearance in the two existing movies, as far as I can tell, are just some dudes in space suits in that early scene in the first movie when the Emperor's Herald shows up, but I also think explaining Guild Navigators as a thing is... well, it's a lot).
Probably the most welcome change is that of the character of Chani, played in these movies by Zendaya. In fact, really we're just talking about her role in the second movie, as she's something of a non-entity in the first one (which makes sense given that she's only literally in the story near the very end - most of her appearances are in Paul's prophetic visions in which she sort of represents Arrakis and the Fremen people, a bit like how Jamis, being the "friend" who teaches Paul the Fremen ways, does so by dueling him to the death).
Chani, in part two, is the voice of skepticism among the Fremen, and fleshes out this group of people as not being just a single hive mind. It's a difficult needle to thread - she's simultaneously the Fremen woman who falls in love with Paul while also the most vocal doubter of his divine nature.
It could be easy to see these two roles as being somewhat contradictory, and maybe better separated out into different characters. But I think that the film somehow makes this work, perhaps because her closeness with Paul allows her to see his humanity - both in an attractive, comforting way, and also in a manner that gives her too much specificity to his character and personality to let her believe he's this more abstract idea of a prophesied messiah.
The movie ends with Chani leaving the palace in Arrakeen on worm-back, leaving Paul after he has demanded Irulan's hand in marriage and sent the Fremen up to bring their jihad to the stars.
What's great is how this functions as a one-two punch to her faith in Paul. While the marriage is of course purely for political convenience - to legitimize Paul's seizure of the imperial throne by making himself a reasonable heir to Shaddam IV - it's nevertheless a reminder that Paul, despite learning the Fremen ways and living the Fremen life, is ultimately a creature of this imperial ruling class, where a bond that should represent a genuine emotional connection and life commitment is merely another maneuver in the grand political chess game.
And, on top of that, he's enabled the most destructive aspects of her culture, knowing full well the death and destruction that it will unleash. She has fought long and hard for her peoples' independence, but what they're going to get is not just freedom from tyrannical overlords, but to become the tyrannical overlords. Paul understands this entirely, but it doesn't stop him from letting it happen.
I know Frank Herbert considered Paul to be a villain, but as written he's more of an anti-hero - the text of the book makes it seem pretty clear that what he does is the lesser of evils, and ultimately all intended to save the human race from extinction. Granted, perhaps we're meant to wonder if Paul's prescience is really all that infallible, and if perhaps he's actually just seeing what he wants to see that will lead him to power. But at least in my single reading of the book, I didn't see a lot of evidence for that interpretation.
But regardless of whether Paul's good intentions outweigh the evils he unleashes, from Chani's perspective, it lays bare the lengths to which Paul will go.
The interesting question, then, is where we go from here.
In the books, Chani plays a similar role that Jessica did for Leto, in that she's Paul's wife in all but name. Paul never has a child with Irulan, and the empress-consort is left politically neutered and emotionally shunned, while Chani is the mother of Paul's children and given the reverence that her lover's position would typically be due.
In the movie, Paul claims that he's foreseen that Chani will have a change of heart, and return to him in time. I wonder, though: is that just a nod to the inevitability of their reunion given how things must go in the future stories?
Again, the book's version of Chani never abandons Paul, and is loyal to the end. But this one is horrified by the things that he winds up doing.
Now just think about what her son winds up doing.
While his rise to power comes with a jihad across the cosmos that kills billions, Paul is still looked upon as a benevolent, messianic figure. But it turns out that this is basically because, at least according to Leto II, his son, Paul isn't willing to go quite far enough.
Leto II is the God Emperor of Dune. At the end of Children of Dune, he allows the Sandtrout (a kind of early phase of the sandworm life cycle - one that I'm not sure totally makes sense as the species seems to subsist entirely on cannibalism, which is not thermodynamically sustainable) to form a kind of exoskeleton over his body, eventually transforming him into a human-sandworm hybrid that rules the Imperium for millennia.
Unlike Paul, Leto II becomes an utterly cruel despot - and he does so consciously and intentionally, with a sort of end goal of weaning humanity from the very idea of divine saviors. By the time he's done, the legacy of the Atreides is as being the worst villains known to humanity.
And yeah, that's Chani's son.
That being said, Villeneuve has said that his ambition is to adapt up through Dune Messiah, the second book in the series, considering it the end of Paul's arc. Paul's children are certainly part of that story, but they don't become central to them until Children of Dune.
So, I kind of wonder what will happen with Chani in the now fairly likely Dune Part Three, and if it will conform or diverge from the books.