UBI could easily become a poverty trap, enough to keep living, not enough to have a shot towards becoming an earner because you’re locked out of opportunities. I think in practice it is likely to turn out like “basic” in The Expanse, with people hoping to win a lottery to get a shot at having a real job and building a decent life for themselves.

If no UBI is installed there will be a hard crash while everyone figures out what it is that humans can do usefully, and then a new economic model of full employment gets established. If UBI is installed then this will happen more slowly with less pain, but it is possible for society to get stuck in a permanently worse situation.

Ultimately if AI really is about to automate as much as it is promised then what we really need is a model for post-capitalism, for post-scarcity economics, because a model based on scarcity is incapable of adapting to a reality of genuine abundance. So far nobody seems to have any clue of how to do such a thing. UBI as a concept still lives deeply in the Overton window bounded by capitalist scarcity thinking. (Not a call for communism btw, that is a train to nowhere as well because it also assumes scarcity at its root.)

What I fear is that we may get a future like The Diamond Age, where we have the technology to get rid of scarcity and have human flourishing, but we impose legal barriers that keep the rich rich and the poor poor. We saw this happen with digital copyright, where the technology exists for abundance, but we’ve imposed permanent worldwide legal scarcity barriers to protect revenue streams to megacorps.

That's way better than the present situation where they just die, though. It's at least a start.