Based in your first two sentences, I think your understanding of UBI is mistaken. You seem to be under the impression that people don't or can't have a job when there is UBI. This is not the case. If you don't believe me, just look at Alaska.

Everyone enjoys some sort of benefit, tax break, subsidy, etc. from the government. UBI is the same thing in the form of a regular, universal transfer payment. Nothing more, nothing less.

I do understand UBI. I was referring to the previous context that AI would introduce mass loss of jobs and overall reduced employment, not specifically to UBI being a replacement for jobs.