System back button no longer suppressed when a custom leading bar button item is set, on iOS 27 iOS 26 and earlier — the system back button is suppressed; only our custom leading item shows. iOS 27 beta — the system back button also appears at the top-left, next to our custom item, and allows an unexpected pop. navigationItem.hidesBackButton = true / .navigationBarBackButtonHidden(true) does not resolve it.