The 50% of the population who are blue collar workers aren’t going to retrain as particle physicist or theoretical computer scientists one they get their UBI.
I'm not saying that 100% of that 50% will be employable in this world. I'm saying that over time that 50% will inevitably become that bare minimum. The way I see it is 150 years ago, your idea would be that we couldn't possibly get all children to become educated at an 8th grade level, yet here we are, even making an HSD the bare minimum.
Eventually your masters thesis will be an area for you to study and pursue to make an attempt at furthering society.