There's nothing wrong with reducing the incentive to work. That simply means jobs that must be done will have their wages rise. Jobs that don't need to be done will disappear.
Define "Jobs that don't need to be done". As Capitalism is ruthlessly profit-seeking, every job currently in place in free markets provides value to somebody. There are some in non-free markets, but that isn't affected by UBI existing.
A job that doesn't need to be done is one which doesn't produce enough value to pay a person enough to do it.
A possible example would be many cast food positions. If the workers didn't have to work together by wages would go up driving up the cost of fast-food. The higher cost would lower demand, and it might not make sense to have 10 fast food restaurants on every block.
I'm going to assume by "pay a person enough" you mean pay a living wage.
But now we're back to one of the key criticisms of UBI - reduced labor supply leads to higher wages but reduced employment, increased prices, reduced economic activity and consequently decreased consumer surplus (which would be a bad thing).
What if the value to someone is keeping people busy and thus not challenging the status quo? Or what if the job is useless to society but still makes some money?
Those are still very poorly-defined (what is "keeping people busy"? what is "useless to society"? Examples, maybe?), so it's hard to say anything about them. That said, I don't see why reducing the labor supply would eliminate jobs like those before other jobs.
I'm just kinda reflecting what I read about a book called "bullshit jobs", where he gives examples like telemarketing and a lot of paper pushing admin positions. Basically anything that society as a whole wouldn't notice disappearing. I've heard criticisms like there's less bullshit jobs than he says there is, but still.
Well, telemarketing isn't useless. It is irritating, but it does provide real value to many companies in the form of customer acquisition (also, it takes a very small number of people to do a LOT of calls, so there probably aren't very many of these). "Paper pushing admin" isn't necessarily useless either - some things are just human-intensive to document or coordinate.
In either case, I don't see anything special about these jobs that would make them the first to disappear in the face of UBI.