This UBI exists today already and it brought the civilization to a halt. I am talking about millions upon million of people who depend on the government one way or another. I include government employees into this category, not just people are simply receiving all forms of welfare, be it actual welfare, social security payouts, unemployment insurance, disability insurance, you name it. It is not all, I include all government contracts into this, all companies that are one way or another receiving money from governments, so this is money that was either taken away by taxation or borrowed or printed and given to the government to bury itself and the larger society with itself. All of these things exist today, all of it is happening, AI is not the catalyst for this, the amount of real productivity that AI allows us to have is negligible compared to the enormous layers of automation that we have in infinite forms. Machines, transport, computers, robots, we have all of this today. AI is not changing the equation, the equation was and is and will go like this: I am unable to do better for myself by myself (regardless of the reasons, real or imaginary) and I demand that others take care of all my needs and more and we must have government provide this (through the government power and force and just basic rule of violence - he, who can deliver the most violence wins, until recently governments were the ones capable of delivering the most violence, I am actually rooting for this equation to change, I would prefer that private individuals manage to deliver more violence than the government, I am just not interested in this type of societies we built here).
UBI exists already, taxation and borrowing and printing money and credit expansion allows for it to exist, of-course the increasing money supply is inflation and it reflects in the rising prices but this has never stopped us for real.