The entire foldable category did 19.6 million units last year after seven years of trying. Apple sells that many iPhones every month. So when the iPhone Duo showed up today, the question was never whether Apple is late. Apple is always late. AirPods came out years after wireless earbuds existed and ate the category anyway. The Apple Watch launched five years behind the first smartwatches, and by 2019 it was outselling the entire Swiss watch industry. In both cases somebody else spent a fortune…