UX/UI designers will use AI as part of their jobs. They'll be able to work at a higher level and focus less on boilerplate. That might mean fewer UX/UI jobs, but more likely the standard for app UX will go up. Companies are always going to want to differentiate their apps.

It's like how, in 2003, if your restaurant had a website with a phone number posted on it, you were ahead of the curve. Today, if your restaurant doesn't have a website with online ordering, you're going to miss out on potential customers.

API developers will largely find something else to do. I've never seen a job posting for an API developer. My intuition is that even today, the number of people who work specifically as an API developer for their whole career is pretty close to zero.