Interoperability means that hardware and hardware related OS capabilities have to be accessible to third-party developers. End to end encryption isn't a hardware capability, it's software. Also, they only have to give them a mechanism to access it, they don't have to remove the already existing security mechanisms like notifying the user that an app has requested access to things user contacts or bluetooth. If users don't want to grant an app permissions that's not the fault of the platform developer.
