Prove? Ehhhh, probably not, but maybe. Provides support for the idea that a true UBI (meaning an actual living wage substitute) will not be generally beneficial to society until we have much higher levels of automation all up and down the production stack, but especially the service sector.

I don't think it really shows us anything about a flat subsidy to everyone though.

There is no labor shortage, that would imply we have too little (skilled) workers, but there has never been as many. If you think workers having some leverage is bad of course you'll be against UBI.