With Grimmel, Drago and Drago's warlords absent from the story, Toothless (and by extension, all of Berk and the Encanto's dragons) have no reason to migrate to the Hidden World for their own safety.
Likewise, with no serious enemies or major threats, the Hairy Hooligans do not need to leave Berk.
Oh, Crap!: While Hiccup spends the entirety of Toothless' date worrying, Mirabel thinking he's being Improperly Paranoid, it's when he notices a piece that had come loose from his artificial tail-fin, meaning it could fail and he would plummet to his death at any moment, do they climb onto Mariposa to try and find him.
Perspective Reversal: An adaptation version. In How to Train Your Dragon: The Hidden World, Hiccup was desperate to make sure he and Toothless can stay together, with his Love Interest Astrid pointing out that he might have to accept letting him go. Here it's the opposite, with Hiccup thinking that he will have to let Toothless leave (since the Light Fury seems hostile to humans), while Mirabel points out that Toothless has too much back at the Encanto he would have to give up if he chose to stay. The Light Fury warming up to them makes it a non-issue.
Pet the Dog: When they return to the Encanto, Alma gives them another day off to enjoy their matrimony before Mirabel goes back to running the place.
