Apple has stopped signing iOS and iPadOS 14.4.1, following the release of iOS and iPadOS 14.4.2 last week.
Older versions of iOS are usually unsigned after later software updates. By stoping signing them, Apple prevents downgrades to previous versions and reduces the chances of jailbreaking.
iOS 14.4.2 includes an important fix for a security flaw that Apple says was “actively exploited”. Users running iOS 14.4.1 or older should update to patch the bug.