Kylo Ren's redemption in Star Wars: The Rise of Skywalker would have been better if a cut scene was in the movie. Over the course of the sequel trilogy, Kylo Ren is torn between the light and dark sides of the Force, obsessed with being Darth Vader's heir apparent. Ultimately, however, his destiny was to fight alongside Rey as Ben Solo, doing his part to help defeat Emperor Palpatine on Exegol. As his final act, Ben sacrificed himself to save Rey, transferring his last bits of life energy to her so she could continue to be a beacon of hope for the galaxy.
The Rise of Skywalker attempts to establish Ben's arc early on by showing he's still troubled by his encounter with Han Solo in The Force Awakens. But since Kylo spends much of The Rise of Skywalker's first half committed to crushing the Resistance and turning Rey to the dark side so they can rule the galaxy together, his turn back to the light came as a bit of a surprise. For some viewers, this plot point wasn't fully fleshed out and arguably could have benefitted from additional attention. There was a Rise of Skywalker scene under consideration that would have done this, but it wasn't in the movie.
The Rise of Skywalker novelization contains a passage where Kylo Ren interrogates a captured Chewbacca aboard his Star Destroyer. Using the Force to probe the Wookiee's mind for information, Kylo sees a slew of happy memories including Chewbacca spending time with Han, attending Han and Leia's wedding, and helping raise a young Ben. Kylo is reminded of when Chewbacca taught him how to pilot a speeder and shoot blasters. The book reveals Kylo called the Wookiee Uncle Chewie in his youth, and he's left nauseated by seeing these memories in quick succession.
One of the reasons why this scene is such a powerful moment is it exposes the lies Snoke (and, by proxy, Palpatine) fed Ben during his corruption. Kylo was convinced Chewbacca never loved him, but the memories reveal the two had a very touching bond when Ben was a boy. They likely influenced Ben turning back to the light; as presented in the film, it appears as if Leia reaching out to her son was the big thing that did it, but in the book her death feels more like the final step in a gradual buildup throughout the story. The Chewbacca scene also illustrates Kylo's inner turmoil and shows he never fully turned to the dark side. If he had, he probably would have blocked out the memories and focused on the task at hand, but he allowed himself to be affected by Chewie's past.
The Chewbacca scene might have been a good parallel to the one slice of Ben's backstory audiences did see in the sequels - the flashback at Luke's temple. Rather than depicting Ben as a frightened boy betrayed by his uncle (making his turn to the dark side understandable), readers are treated to a much happier period in his life, actually seeing an instance of Ben experiencing joy with a family member. Had this been in the movie, Kylo's arc might have been more impactful. It's one thing for Han or Leia to express their feelings for Ben in dialogue, but a quick montage of Ben's childhood would have been poignant and shown his childhood wasn't as troubled as some might have believed. It's unfortunate there wasn't room for it in the Rise of Skywalker movie.