We also have the problem that people are forced to evaluate what activities would be productive for them in terms of the money paid to them, but it's debatable whether the aggregated signals of demand in a given economy truly reflect what people would believe are "important" or "needed" or "valuable" activities (using scare quotes specifically because
obviously the whole debate revolves around how to determine the meaning of these types of terms).
My mom is an example. She works a highly menial and thankless job at a rural county courthouse in the Midwest, where she is paid an extremely small salary, given very few benefits, very little vacation time, and has no prospect for retirement, regular raises, career growth, etc. The courthouse could operate with probably 25% of the current staff, but they keep headcount artificially high because state funding and other programs depend on how many employees they have.
Largely, my mom is paid money to endure slight sexual harassment from small town attorneys and judges, and to do a tiny workload of clerical work. And the amount of money is barely enough for basic living in her area, even after accounting for the lower cost of living there.
It seems bang obvious that her employment is inefficient. The same exact thing happens for thousands of people in her area, whether in government, school jobs, private companies. There's just a ton of excessively meaningless work that companies or employers have ulterior reasons to sponsor with a paycheck even fully knowing that the labor itself is not productive or necessary at all.
I think if my mom knew she had a reasonable guaranteed basic income, she would volunteer her time at the local hospital, deliver meals to sick people, do more productive labor around her own home or through child care provided to my siblings and their children, perhaps create craft works to sell online, etc.
The net result could easily be that her overall labor productivity in the big picture sense would go way, way up after she is free to quit the essentially pure loss menial job and focus on things where she knows she can add actual, obvious value for people.
Unfortunately, I think most developed nations suffer this problem. Lots of jobs exist because of weird misaligned incentives on the part of the employer, who could truly not care less about the actual labor productivity of a bunch of employees and has them on the payroll for totally separate reasons.