It's not necessarily extraction from those that do work for a living if the tax to pay for the UBI is largely a wealth-tax taking the majority from wealthy investors (who, by the conventional wisdom of capitalism, do exactly what you accuse and extract time and output from those that do work for a living for the "hard labor" of managing an index fund). If that tax is balanced to offset the two, well - you've got a fair society (and one likely to eliminate billionaires over time).

I estimate that wealth tax price to be around the average cost of living - as any less and those are people who have no choice but to accept whatever poor labor deals are put in front of them, which enables the capitalist to extract more value than the labor is worth. If people have their costs of living covered and freedom to pick and choose to labor or not, then it doesn't matter if your net worth is 10k or 10M, you're going to accept a similar wage for similar work. (well, not entirely - but at least at that point it's about desire for luxuries not hard desperation)

A truly Communist economy takes this much further and splits things evenly from the start. Though I'd argue you get there with a very-high wealth tax and UBI. That doesn't necessarily mean the society is producing a lot of goods though - especially if you just uplifted most of your citizenry that were only doing those shitty jobs because they would literally starve otherwise. But to communism's not-credit, there haven't been many great implementations solving the motivation problem yet either.

I suspect a gradual UBI/wealth tax combo is going to do a lot better at easing in motivation and crucially - preventing violent backlash from those in power - than any sudden shift to a fully-communist system. Personally, that is.