MMT would suggest that the government prints money and then adjusts taxes to control inflation.

So you have a bunch of new people move, they start collecting UBI, the government prints money to fund the new liabilities, the newly-immigrated spend their UBI, incomes/revenues go up for businesses, the overall size of the pie grows, and if inflation starts to get out of control you raise taxes such that everyone is still better off than before.

Unfortunately this wouldn't work because of politics. You need a relatively reactive monetary & tax policy which just is not realistic.

But what happens when you can't raise taxes any further? Or the high taxes shrink the motivation of the people running businesses to expand their businesses.

The money has to come from somewhere or you _will_ have runaway inflation.

They spend what they get - few people surviving on $12k/year are saving much. So do the people who sell them stuff, as do their providers, and so on and so forth. At every step, some taxes make their way into the state's coffers.

https://en.wikipedia.org/wiki/Multiplier_(economics)

Eh, this doesn't really work well with too much immigration running in to land and water use issues, along with uncontrolled need for infrastructure expansion.