Lots of stuff is going on at the end of your novel. There’s action and revelation and emotional upheaval. But it all must be presented in terms of what’s happening to the people.
Ideally, your characters will be proactive. There’s probably a whole other blog post in that. Characters who have stuff happen to them are far less interesting than characters who make stuff happen. So, as much as possible, rely on character action and agency rather than circumstance and accident. This is true throughout the story, now that I think of it, but it’s especially important in your climax and denouement.
No time to stop and think
Character rumination needs to be kept to a minimum at all times, but especially at the end. Characters sitting around thinking about stuff is boring, even when Dan Brown does it, as in Lost Symbol. Yes, we sometimes need to know what the characters are thinking. We don’t need to know it all at once, and we don’t need it in great whacking chunks.
If your whole book is an arrow driving to a final destination, then the climax is the widest part of the arrow, and the denouement is the finely honed point. Don’t blunt that sharp edge by ramming it up against swaths of expository rumination.
Echo the opening
Circularity is a rhetorical practice of ending with something similar to the beginning. You’ll see this a lot in nonfiction — Dan Pink’s TED talk, for example. This is also possible in fiction.
Lord of the Rings begins and ends in Hobbiton. The Shire and, indeed, the entire storyworld has changed drastically, as have the characters. But Tolkien brings his epic full circle by returning to the point of beginning.
Sometimes the events of the story make it impossible, or at least unrealistic, to literally return to the opening setting. That’s okay. You can find subtler ways to echo the opening. If you have multiple POV characters in your story, consider beginning and ending with the same POV character. An object, a turn of phrase, a season of the year…anything that you can bring in at the end to mirror or remind the reader about the opening will do, even if all it does is show just how far they’ve come.
Maybe that should be especially if it shows how far they’ve come.