Increase Total Factor Productivity so that there's still just as much stuff to go around even with fewer people putting in less work to make the stuff.

Forget UBI and implement UBS instead. Income is an unnecessary artifact in accessing services.

Who or what will provide the services and how do you incentivize them or it?

In this hypothetical, AI / robotics automation I suppose.

AI+Robots. They need as much incentive as your laptop or phone to do as asked.