What is implemented in the BFF layer when it is assumed that this is an API Gateway?

Question

API

Greetings!

I heard a lot that one of the options for implementing the API Gateway is Backend for Frontend.
But I do not quite understand what the implementation of BFF is in the API Gateway layer.
Are they just routes that lead to the service that implements the frontend?
Or do you need to implement the logic for building the visual part for the client right in the API Gateway layer?
For example: building and rendering an application on React, or implementing the MVC pattern on templates.
Or is BFF simple and stupid: a situation where we make a separate API Gateway for each client?

Answer 1

Not stupid, but yes, for each api front that provides the features it needs. Also, there may be different operations and additional data transformations that are needed only for this front.