I find research like this a bit confusing. "Providing people with unconditional monthly payments improves mental well-being" feels almost self-evident. Most people’s mental health would improve with more financial security. I have a decent income, and even I would feel better with an extra $1,500 a month.
Make no mistake, this is not UBI. It is welfare/subsidisation by the taxpayer who actually brings in income. UBI is, well, universal. "UBI" that is not universal is welfare.