Apple has ceased signing iOS 11.4 following the release of iOS 11.4.1 on July 9. This means iPhone, iPad, and iPod touch users that have upgraded their devices to iOS 11.4.1 will no longer be able to downgrade their devices to the previous iOS version.
This is the norm with Apple, who routinely ceases signing older versions of their operating systems after releasing new versions. This encourages customers to keep their device’s operating system current.
iOS 11.4.1 is likely one of the last updates to iOS, as iOS 12, the upcoming new version of Apple’s mobile operating system, is currently in beta testing by developers and public beta testers. iOS 12 is expected to see release this fall.