More money (provided by UBI) chasing fewer resources (less reason to work) until a new equilibrium is reached.

Somebody has to farm, and it’s not easy work.

Sellers are incentivized to charge as much as the market will bear.

Suppose you have a market of 1 person and he has $10 to spend on pork per month. You as the pork producer will charge $10 for a months supply of pork (if you can profit). Suppose that is how things go.

Now you learn your customer has $20 to spend on pork thanks to an increase in government benefits. The customer is feeling much better about himself. But Whoopee, you can suddenly charge $20!!

The customer now has a dilemma: either give you his increase, or go without pork. He choose to continue buying pork. He is no better off, it just enriches you the seller.

Now this is not perfect - it’s quite possible some new pork farmer may enter the market and charge $15. But more money tends to just shift price points up.

What actually lowers real prices is shifts in supply (offshoring, crop yield technologies, etc).

Consider an even simpler example, your own spending. If you suddenly gained $2k per month more, that’d be great! You could save, or buy something nice etc. but your consumption will largely remain the same - you still need housing, food, transit, etc. what if those suppliers just happen to increase prices at the same time? Are you really going to change your patterns? Probably not especially if it’s all suppliers, like we saw with covid. Everything got more expensive but everyone kept buying because they still need what they need. And if there was suddenly an increase in government benefits, you can safely bet most suppliers would raise prices as much as they can.