Group 1 - Apple has stopped signing iOS 18.5, meaning users who upgraded to iOS 18.6 can no longer downgrade to the previous version [1][3] - iOS 18.6 was released over a week ago, focusing on security updates and addressing more than 20 vulnerabilities [3] - The signing process is a verification check conducted by Apple on its servers when downloading a new iOS version, ensuring users install the latest security improvements [3] Group 2 - The cessation of signing for iOS 18.5 is part of Apple's strategy to ensure customers have the latest security enhancements and are protected from known attacks [3] - Apple typically stops signing old software about a week after releasing an update, reinforcing its commitment to user security [3]