https://wccftech.com/amidst-ios-14-6-excessive-battery-drain-issues-apple-blocks-downgrading-to-ios-14-5-1/

Apple updates tend to have an impact on the battery life of old and new iPhones. However, the latest update has gathered enough traction as many users are experiencing excessive battery drain issues. In the middle of these concerns, Apple has stopped signing iOS 14.6 which makes it impossible for users to downgrade to iOS 14.5.1.

iOS 14.5.1 was released at the beginning of May that housed numerous important security updates and a bug that disallowed users to see the App Tracking Transparency prompts. However, Apple has decided to block users from downgrading to iOS 14.5.1 from iOS 14.6 today. Apple usually stops signing iOS builds a week after the new version is released.