Apple today stopped signing iOS 18.0, preventing iPhone users who have upgraded to iOS 18.0.1 from downgrading to iOS 18. Apple released iOS 18.0.1 a week ago on October 3. It is not unusual for Apple to stop signing older versions of iOS within a week or two after a new version of iOS is released. When Apple stops signing an update, it can no longer be installed on an iPhone due to a...