some will be writing novels, or starting bands, or making community gardens, or teaching, or whatever.

And slaves in 3rd world countries will make all the things (cameras, phones, clothing, furniture, raw materials etc.). Are those gardeners actually going to contribute in any way to the lives of people in China who make the things that help them be a gardener? Trade is a 2 way street. Person in China makes the things, but what does the American gardener do in return for the Chinese maker?

  UBI gives people the ability to follow their dreams without risk of homelessness and starvation.

This is what independently wealthy have today. But, the way those people make money is by subjecting everyone else to wage slavery, creating monopolies and extracting rent. Sometimes it's fraud. In the past it was explicit slavery.

So, maybe Americans could live like poets and gardeners, but first the rest of the world would have to be enslaved. Meaning, you don't trade with the Chinese and provide value in return, but enslave them. Is this a possibility? Do you think Chinese makers are going to put up with American poets and gardeners on welfare?