People would certainly keep working with UBI. The concept is to just ensure a minimum quality of life for everyone. Think enough money for a small studio apartment, a very basic grocery budget, and a small budget for incidentals. Enough that you can always keep a roof over your head and food in your belly. And health care covered by a universal healthcare plan.

The thing is, most people don't actually want to live like that. Most people don't want to live in a studio apartment their whole life. They want space to relax, pursue their hobbies, have space for kids, etc. Living a pure-UBI existence would be pretty spartan. UBI wouldn't be high enough for that, unless we start considering cases of extreme automation where no one really needs to work anymore.