I thiiiink the thing with UX is that they consider overall usability and click paths, while UI is more down in the reeds and looks at more specific things like alignment, design language and color choices. The line between seems pretty blurry though, and how it works in practice probably differs widely between companies.

A good UX/UI team can make or break a project. As a Frontend-focused software dev, that kinda hurts admitting. It's just always very frustrating to deal with them, because designers are specialized in design. So they neither know about technical limitations that make trivial seeming things hard (like conditionally changing a buttons color based on server state) but they also don't know about technical "freebies" that the libraries we use give us (like just telling a component that they can overflow and render things wherever you want in ways that Figma would never allow you to design). So talking to them is hard, which leads to a spiral of never talking to them, fucking up the UX, and then dodging them while they try to get the UX fixed. That just sucks for everyone involved.

Hating the Design Team is apparently such a universal experience that Josh W Comeau has a great article on it. Really worth the 15min read, if you want to improve your relationship with the design team!