Apple has stopped signing iOS 15.0 after the October 1 release of iOS 15.0.1. This was the previous version of iOS which saw a public release September 20. iOS 15.0 is no longer signed. It is impossible to downgrade to this version if iOS 15.0.1 has been installed.
Apple stopped signing iOS 14.8 last week. This means that iOS 15.0.1 is no longer publicly available. Users who have upgraded from iOS 15 can't downgrade to iOS 14.
Apple regularly stops signing older software updates once new releases are out to encourage customers to keep up-to-date their operating systems.
iOS 15.0 is a major update that introduces Focus Mode, Live text, on-device Siri and iCloud+. Safari changes are also included. More details can be found in our iOS 15 roundup.
iOS 15.0.1 introduced a fix to a bug that prevented authenticated Apple Watch users from unlocking an iPhone 13 model while wearing a mask. It also fixed a bug in the Settings app that could incorrectly display a storage alert.
