The basic cornerstone of international trade is the idea that exchanging your goods for someone else's is almost always cheaper than producing everything yourself. Let's say Russia is good at producing coal and wants grapes. Let's also say that Italy is good at producing grapes and wants coal. Sure, Russia could grow its own grapes and Italy could mine its own coal, but their lack of proficiency when it comes to producing those things increases costs. However, if Russia agrees to produce coal for Italy and Italy agrees to produce grapes for Russia, the costs of the goods go down for both countries because of the proficiency of the exporters at producing them. A similar logic applies to workers and consumers.
Let's say that you're really good at cooking but you can't be a cook because it doesn't make you enough money to survive. Instead, since you're okay at math, you become an accountant. Let's say that I'm someone who likes eating at restaurants but also needs someone to manage my finances, and happens to hire you. Because you were forced into accountancy so as to not starve (how ironic), I've had to trade an excellent cook making my meals for an average-level accountant managing my finances, an obviously bad trade. But if UBI was implemented, you would be guaranteed a roof over your head and food in your belly at the very least. With your primary concern of survival dealt with, you could afford to follow your dreams and become an excellent cook. In turn, I would both benefit from your cooking proficiency and have a position open for an actually skilled and passionate accountant to take. Just as lowering the barriers to international trade like tarrifs lowers prices, lowering the barriers to those following their dreams like the worry of survival increases labor quality. In essence, enacting UBI means that everyone wins (except the oligarchs who'd be paying for it, but fuck them)!