Apple released iOS 14.5.1 yesterday, and as is traditional, Apple has now stopped signing iOS 14.4.2, making downgrading to that version of iOS no longer possible.
Apple’s release notes say the iOS 14.5.1 update fixes a bug with App Tracking Transparency that may have prevented some users from receiving prompts from apps.
This update fixes an issue with App Tracking Transparency where some users who previously disabled Allow Apps to Request to Track in Settings may not receive prompts from apps after re-enabling it. This update also provides important security updates and is recommended for all users.
Apple is known to routinely stop signing older versions of operating systems after it releases a public update, as part of an effort to encourage users to keep their devices’ operating systems up to date. Restoring devices to older iOS builds is common for users with jailbroken devices.