My experience is that SPAs have been the way to make frontends, for the last eight years or so. May be coming to an end now. Anyway, contact with the backend all went through an API.

During that same time, the business also wanted to use the fact that our applications had an API as a selling point - our customers are pretty technical and some of them write scripts against our backends.

Backenders read about API design, they get the idea they should be REST like (as in, JSON, with different HTTP methods for CRUD operations).

And of course we weren't going to have two separate APIs, that we ran our frontends on our API was another selling point (eat your own dog food, proof that the API can do everything our frontend can, etc).

So: the UI runs on a REST API.

I'm hoping that we'll go back to Django templates with a sprinkle of HTMX here and there in the future, but who knows. That will probably be a separate backend that runs in front of this API then...