If they really wanted to answer the question, they'd have to gather several millions of dollars, and then go to some island somewhere and provide UBI to everyon

If they really wanted to answer the question, they'd have to gather several millions of dollars, and then go to some island somewhere and provide UBI to everyone (without publicizing it, if at all possible). Then observe the changes in that group of people. For best results, choose an island in a developed part of the world.