"That said I believe front and backend should work closely together. There is no reason that the frontend should be blocked because the API design can be figured out before the backend is written and the frontend can mock out the missing features until they are available."
Came here to say exactly this. At my current workplace, one of the very first steps in any project that involves both FE and BE work is for FE and BE engineers to get together and design the API. Once that's done, work can proceed on both sides in a largely asynchronous and independent manner. And one of the first things to be implemented on the BE is API endpoints with multiple mocks that can be requested by the FE, so the FE can start integrating with the endpoints as early as possible.
Came here to say exactly this. At my current workplace, one of the very first steps in any project that involves both FE and BE work is for FE and BE engineers to get together and design the API. Once that's done, work can proceed on both sides in a largely asynchronous and independent manner. And one of the first things to be implemented on the BE is API endpoints with multiple mocks that can be requested by the FE, so the FE can start integrating with the endpoints as early as possible.