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 server-side software verification check that happens before new software is installed, so those who have upgraded to the latest version of iOS 18 cannot downgrade to iOS 18.0.
Apple prevents downgrading to older versions of iOS to encourage iPhone users to keep their operating systems up to date with the latest security fixes. iPhone 16 users who have upgraded to iOS 18.0.1 can no longer install any older software, but iPhone 15 and earlier users have the option of downgrading to iOS 17.7, which is also still signed.
The iOS 18.0.1 update addressed bugs with the touch screen, Camera, and Messages app, plus it fixed two vulnerabilities.
This article, "Apple Stops Signing iOS 18.0" first appeared on MacRumors.com
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