I would say as a graphic designer sometimes solves the most basic problem:
communicating an idea. Sometimes this means “how to create a certain emotion using colours and photography” or “how to relate a metaphor using only a few symbols and words” or “how to convey all this textual information without losing the viewer’s interest” or “how to get the viewer to think of something, without telling them to think of that something".  Sometimes the arising needs and objectives of a product become the problems that graphic design seeks to solve using design principles like colour, typography, composition, etc.

So far, I solve user problems, business problems and technical challenges. We talk to their users and/or gather data about users, we iterate, we even test my designs.