It might be helpful to view this from a scientific research perspective. UX research is more about how things should be done to provide a better usability for the user. Like, general respectively abstract concepts (e.g., how should a chatbot present itself when it first "talks" to the user, which UI components could be involved). It's not about how to actually design those things, i.e., applying CSS to an HTML document if you will. UI design is mostly a dev job, while UX design is more of an actual research discipline.