Knowing how to do it through the CLI adds nothing to your understanding of the concepts though. Its just whether or not you have to remember an opaque CLI command, or you get a UI to click
I think it depends. If the GUI tooling is exposing you less to the actual concepts and builds new concepts on top, that simplify things, then that will hamper a new user's understanding of the underlying concepts. Of course, it is not the CLI usage itself, that is the key here, but the usage of a tool, which exposes you to the actual concepts of git, and the most common tool like that is, of course, the default git command line interface.