If that's true (and only the app who stored the item can retrieve it) I wonder who is responsible for GDPR regarding its storage. Is the app responsible? But i

If that's true (and only the app who stored the item can retrieve it) I wonder who is responsible for GDPR regarding its storage. Is the app responsible? But it cannot even access the data after it is deleted. Apple? They have no idea what the data is. User? They don't even know about the data and cannot access it either. No one?