My experience working on "medium sized" B2B apps in 10-20 people teams is that the cleanest way to design API-s is to have a regular REST API for the basic CRUD operations on the entities, and then have more specialized endpoints for specific pages, tables, dashboards etc. on top of that. Having specialized endpoints is kind of required, as the data often needs to be searchable, sortable, filterable and paginated, which would be pretty wasteful, or sometimes even impossible to do on the frontend. I find these kind of REST API-s pretty straight forward to design and implement for the most part, and as others pointed out, onboarding is extremely easy if the new developer on the team has worked in software dev at least for a year or two. This also makes it pretty easy and quick to transition to a fully public API if needed (although I have rarely seen this as a requirement).
Edit: fixed a typo.