You are very clearly being sarcastic, but the only reason that UBI like this wouldn't work in the scenario being described is because the already-mega-wealthy owners of the AGI hardware and software decide that they want to have all the money instead of actually making the promise of automation real for all of humanity.

And to be clear, there is no conceivable universe in which that extra money would make their lives better in any meaningful way.

They could support high taxes on the money they earn through the AGI, to fund a UBI that would support literally everyone—because their products are doing literally all the work necessary to maintain a civilized society (barring some in-person tasks that it's hard to hand over to even a very smart robot) without any human actually needing to do any work. They could do so without making themselves poor, or even the least bit less comfortable.

The reason they would choose not to is because they're corrupt selfish "rugged individualists" who care more about their dollar-denominated high scores than about literally any other human being on the planet. And we know this because that's the case with the people in the closest-analog positions today.