Work expands to fill all available time. Make less time available and there will be more pressure to stop doing useless work.
Meanwhile the reason that people become nurses instead of social media managers is that nurses are paid more than social media managers and simultaneously attract people who want to feel like they're doing something meaningful instead of something useless, both of which would continue to be the case.
It's also obvious to me, that anytime any worker feels financially comfortable to stay home, a huge chunk of them will inevitably be hijacked by algorithmic feeds. Everything else is just some version of "pick yourself up by the bootstraps".
I am expecting Social Media Managers to be paid hand over foot to handle this transition even though they might find other work more meaningful (much like Real Estate Agents now, who would rather be doing something else, but the money is too good).
These are not reasons not to do UBI, but if there is economic devastation after, you can expect a quick reversal and a generation-wide flopping of the idea. So might as well fix these underlying issues as you do UBI.