Apple has gone on an un-signing spree today. The company has to sign a version of iOS for user to be able to install it and usually continues to un-sign the firmware for a few days after releasing a new version of iOS allowing users to downgrade using a computer if there are any major problems.

Jailbreak users often use this to downgrade if they are awaiting a new Jailbreak release. Today Apple has stopped signing several iOS versions:

iOS 12.4.9 (16H5)

#tvOS 8.4.3 (12H903)

#iOS 14.2 (18B92)

bridgeOS 4.6 (17P6610)