The problem with UBI without demanding some labor in return is that it is extremely inflationary but hinders the ability of workers to demand more from employers in wages/benefits. Because employers could gain a workforce without meeting inflationary increases, the UBI payments would have to increase or the labor/capital balance would be drastically shifted. This would lead to even more inflationary pressure without adding productivity or reducing profits.
Also, since all UBI schemes get mired into "pay for" debates the bulk of those pay fors come from reductions in safety net spending, making labor even more subservient to capital once the UBI payment falls $1 below the real cost of living. This is why right-wing economists, such as Freidman, loved it. It simply uses the workers as the medium to funnel state created money to the upper class that is extremely adept at evading taxation.
None of the UBI schemes I've seen account for the vast amount of required labor to maintain the social economy, such as mitigating climate damage or caring for those unable to contribute to profits. A short walk around any large city or small rural community will show that this deficit of labor is already extreme and threatens to erode the social contract, being dependent upon volunteerism.
I would suggest making that volunteerism, anything that benefits the greater good of society but not profitable to a private sector business, a paid position with a federal job guarantee. Such a guarantee would include a livable wage and benefits, so it would create a bottom for private sector employers as well.
Such a program would be counter-cyclical to the business cycle with participation increasing or decreasing as the business cycle varies. This would also inject federal money specifically when and where it is needed automatically and take a great burden off states and communities that don't have the luxury of creating US dollars on demand, which is the monopoly of the federal government/Congress.
If this guarantee was administered at the state or local level it could target specific needs of those areas without the cos burden falling on entities already struggling. Only the funding and general oversight of the program would come from the federal government, as each community has its own needs and standards. As the business cycle picks up in an area the participation rate in the program would fall, overcoming the inflationary pressure that a UBI would cause. Employers would only have to overbid the program's wage and benefit offering to enlarge their workforce from a stable of "employed" workers with all of their job and social skills intact.
