As PP have said UC is designed to incentivise working.
Theres often an amount that you are allowed to earn before it effects your UC. And then the UC gradually tapers away as you earn more.
In strict monetary terms you are always better off working.
Peoples lives are more complicated than the UC calculation of course.
Theres often other considerations like the costs of taking up work, caring responsibilities, increased stress of working longer hours etc...that might mitigate against that incentive for individual people.
Thats particularly true at the edge between being entitled to UC or not.
This is true of every benefit. Its impossible to design a syatem that doesnt have some kind of "cliff edge" or "benefits trap". A bite point where people will ask themselves whether losing their entitlement to benefit is "worth it" to them.
What people tend to forget is that under previous systems this kicked in at a much lower income level. And in a much more brutal fashion.
Under the old Income Support you had people (particularly single mothers) trapped on very low levels of benefit for very long periods of time because taking work of any kind would cause all the benefits to stop, losing whatever security they had.
Often, it was impossible to earn enough to cover childcare so working was not even a possibility.
Under Tax Credits and now Universal Credit people are making these sorts of decisions at a much later point. Often when considering moving from part time to full time work. Thats an improvement. More people are able to work, less children are growing up in poverty and more mobey is circulating around the economy.