Core Insights - Apple has officially stopped signing iOS 18.6.2 and earlier versions, along with iPadOS 18.6.2 and tvOS 18.6, meaning users cannot downgrade back to the iOS 18 series after upgrading to iOS 26 [1] - The iOS 26 official version was released on September 16, featuring a new "Liquid Glass" design language and marking Apple's first unified version number across all platforms [1] - The cessation of support for older versions follows Apple's standard practice of terminating support after the release of new security updates [1] Security and Vulnerability - The Ministry of Industry and Information Technology issued a warning on September 10 regarding a critical vulnerability in iOS 18.6.2 that could lead to unauthorized access, which has already been exploited in cyberattacks [1] - Apple aims to encourage users to adopt the new version that addresses these vulnerabilities, although users can still choose to remain on the iOS 18 series [1] User Guidance - Users upgrading to iOS 26 will lose the option to downgrade, prompting experts to recommend backing up data before upgrading and considering the balance between new features and system compatibility needs [1]