This only hypothetical works in a closed system. As soon as money can leave the system it fails. For example taking your UBI cash and buying all your clothing from China. At some point the wealth simply leaves our system and enters there.

Second issue is the price of things will likely get horribly distorted. Let say we need plumbers, no one wants to be the plumber so the cost of a plumber goes way up, to the point no one on UBI can afford to have thee pipes fixes. Now plumbers are incredibly wealthy and in short order we once again have massive income inequality, and basic things like running water can become unaffortable. God forbid no one wants to be farmer. There is no a UBI fixes that issues.

Along the same lines there is the issue of people who just make bad choices. Lets say we can remove food stamps because we have UBI. Now people are spending every penny they have lotto tickets and booze and they don’t have money for food. Do we have to let those people starve and die out of the system?

It seems a success implementation of a UBI would have to be incredibly harsh. Or have some resource that outside people are going to give you money for.

Several Middle Eastern nations have a UBI because they can sell oil, which requires very few workers but generates huge cash (not wealth). When those counties citizen would no longer work they bring in 3rd country nationals to do the work.

I would suggest you look into Qatar for an example of a UBI country, and reconsider what happens in these systems.