Here's just some of the things that become non-trivial in such a scenario:
* Validation - you either replicate the same rules on the generalized API/BFF/FE and risk inconsistencies or figure out a way to extract that validation to a shared package
* Making API calls inside the BFF - usually generalized APIs have a lot of features in individual endpoints, some of which aren't always documented so you'd need a really good documentation that gets constantly updated or some kind of a connector package that makes it easy to discover those features
* Testing - most of your endpoints are just calls to another API, all you can do is mock those calls in your tests based on what you expect the API to return but this gets hairy if you're just copy pasting the same 200 line JSON body across multiple tests so you'll need some helpers/a package for that too. It also requires that you always have a person on your team who's very familiar with how the API you're making calls to works so you don't make false assumptions
You either need someone who's aware of every little detail that goes on in both the generalized API and the BFF or you need all of these constant abstractions to be able to scale properly in any shape or form without introducing bugs with every new feature.
* Validation - you either replicate the same rules on the generalized API/BFF/FE and risk inconsistencies or figure out a way to extract that validation to a shared package
* Making API calls inside the BFF - usually generalized APIs have a lot of features in individual endpoints, some of which aren't always documented so you'd need a really good documentation that gets constantly updated or some kind of a connector package that makes it easy to discover those features
* Testing - most of your endpoints are just calls to another API, all you can do is mock those calls in your tests based on what you expect the API to return but this gets hairy if you're just copy pasting the same 200 line JSON body across multiple tests so you'll need some helpers/a package for that too. It also requires that you always have a person on your team who's very familiar with how the API you're making calls to works so you don't make false assumptions
You either need someone who's aware of every little detail that goes on in both the generalized API and the BFF or you need all of these constant abstractions to be able to scale properly in any shape or form without introducing bugs with every new feature.