It is pretty much a universally-accepted fact that a story in which the characters lead perfect lives and nothing goes wrong is unsatisfying to readers. The high degree of unrealism (?) is naturally frustrating to its audience.
Even children’s books contain at least one central problem to be resolved. And you could argue that children are the most likely to accept an unrealistically perfect story. Here the concern is not of reader satisfaction, but of not wanting to accidently teach kids that a conflict-free life is possible.
However, a story’s ending is where the topic of closure becomes very interesting.
For the most part, I would say the most satisfying ending is one in which a central piece of tension is given full resolution and closure, while secondary sources of narrative conflict or tension are only partially resolved, allowing readers to imagine what comes next and how they may be resolved in the future.
Of course, this is not a hard and fast rule. Books with complete closure at the end do exist, and some are loved by readers. There are certain genres (and even stories that work well like this on a case by case basis) where every character ends up getting exactly what they wanted all along, and even though readers can acknowledge the suspended reality of that, they find themselves tearing up over how happy that ending makes them.
And this is where a writer’s artistic mind must sense what kind of closure is best for their story. In imagining each potential ending, what is the emotional response? How do you want your readers to feel when they read that final line? And how can you stay true to your characters? Is the ending in alignment with who your characters are?