I am sort of torn between the ideas of a Guaranteed Job and Universal Income. The idea that you must work, are forced to work, when someone else eventually decides what that job must be, is demeaning. On the other hand, a society where nobody "needs" to work can lead to a society that isn't socially connected. Or possibly some needed things don't get done (garbage processing?).
I retired at 55 (lucky me!) with a relatively good pension. My basic needs were all covered, with a bit extra for mad money. But I found it became boring. So I started up a small business, serving a need for many. Minimal investment. Soon it grew to 8 or more hours a day, as much as I did when "working full time". But I enjoy those working hours, more than I ever enjoyed the hours I spent working for someone else. I call the shots, I decide how "hard" to work, I select the priorities, and I can decide when to stop. I always have the basics covered through my pension.
This pattern is not unusual. May people that no longer "need" to work, will find something productive to do with their time. If not a sideline business, then volunteering or other things they see as needing to be done. I have met many people like that over the years, more so since I became a part of that circle. Often enough, we end up kicking around other ideas on what else can be done, or needs to be done.
So I suspect that even with just a UBI, enough people will "want" to do things. Society will not fall apart. Things will get done. Large scale stuff will end up being automated, while individuals will discover and implement small scale stuff (some of which may migrate to large scale). Ingenuity and creativity will become the "credentials" people strive for, much like the attitude entrepreneurs have today.