It's also worth noting that you can easily discover which DSpace REST API endpoints are used by the User Interface using your browser. Just open up the DevTools and look at the Network tab. Then perform some action in the User Interface and you'll see every REST API call it makes. This is possible because the User Interface runs entirely in your browser, so it has to make requests to the REST API to gather all data to display & those requests always appear on that "Network" tab.