https://wccftech.com/apple-stops-signing-ios-14-downgrade-from-ios-14-0-1-no-longer-possible-heres-what-it-means/

Apple has seen fit to release iOS 14.0.1 and shortly after a week the company has stopped signing iOS 14. What this means is that users will no longer be able to downgrade from iOS 14.0.1 to iOS 14. Apple usually stops signing a firmware a week after it releases its subsequent update. The company has several reasons for this and one of the main reasons is that Apple wants users to stick to the latest build.

As mentioned earlier, Apple has stopped signing iOS 14, the launch version of the operating system. The move will restrict users on iOS 14.0.1 to downgrade to the previous version. While there isn't anything wrong with it, signing the firmware holds more importance for users who are particularly interested in jailbreaking their iPhone or iPad.