As I see it, a well-designed UBI enables universal employment. It allows people to do the types of work that are not financially recognized in our current system, despite being massively valuable to society (things like taking care of kids and elderly people and continuing education). But I think you are touching on something more nuanced, which is the importance of work (of some sort) to provide a sense of self, usefulness, and meaning in our lives. It begs the question, under what circumstances would people be motivated to work, even if they weren’t required to do so?