In the EU there's a "Computer Programs Directive" which grants us the right to go as far as to reverse engineer any licensed software for the purposes of interoperability.

https://en.wikipedia.org/wiki/Computer_Programs_Directive

Reverse engineering APIs is fair use, not simply using APIs. Eg when Google implemented their own implementation of Java APIs, that was deemed fair use. Google only copied the interface. The courts ruled you can build a competing product that copies an interface for compatibility, just like Compaq did with IBM’s BIOS. Google absolutely would have been on the hook had they used Oracle’s implementation of the APIs.

The distinction is between using APIs (documented or undocumented) vs using and distributing 3rd party libraries and SDKs.

It's likely that in order to avoid distributing Apple IP one would need to reverse engineer some undocumented APIs, but that's coincidental.