> Are you assuming that all these people also have employment income on top of their UBI

Any system with UBI requires other sources of income to exist (thr absence of such sources means that nothing of value is being produced for exchange, in which case any money printed is basically monopoly money and how you distribute it doesn't matter because it isn't doing anything), and a major premise of UBI has always been that it enables those transitionally deprived of income more freedom to reconfigure their lives and ramp up these sources of income (and does so with less redundant—with the progressive tax system—bureaucratic overhead) than do means- and behavior-tested welfare programs.

The particular mix of available other forms of income between wage labor, independent business, or capital don’t really change the basic arguments.

Well, my question implies that being a landlord would be a remaining source of income, for starters. But if that landlord also owns the automated farms and factories producing consumer goods without labor, then the people they're renting to really might not have any other income. At any rate, where a UBI is substituting for employment income that someone used to earn, but is no longer able to, then I don't think the renter gains purchasing power to pay more for rent. (They do gain free time though).

Yes, if you have a single capital owner that owns all productive assets, that's a serious problem that UBI won't solve.

The idea of adopting a downward-redistributive policy like UBI is to do it before that occurs.