Following iOS 15.6 release Apple now stops signing iOS 15.5. This prevents devices from downgrading to previous iOS releases.
Reference: Apple Stops Signing iOS 15.5 Following iOS 15.6 Release, Downgrading No Longer Possible
Following iOS 15.6 release Apple now stops signing iOS 15.5. This prevents devices from downgrading to previous iOS releases.
Reference: Apple Stops Signing iOS 15.5 Following iOS 15.6 Release, Downgrading No Longer Possible
Following iOS 15.4.1 release Apple now stopped signing iOS 15.4 preventing downgrade on devices.
Reference: Apple Stops Signing iOS 15.4 Following iOS 15.4.1 Release, Downgrading No Longer Possible
Following iOS 15.4 release Apple now stopped signing iOS 15.3.1 preventing downgrade on devices.
Reference: Apple stops signing iOS 15.3.1, blocking downgrades from iOS 15.4
Apple now no longer signs iOS 15.1.1 preventing downgrade from iOS 15.2.
Reference: Apple stops signing iOS 15.1.1, blocking downgrade from iOS 15.2
Apple stops signing iOS 14.7 preventing downgrade from 14.7.1. Apple typically stops signing older released from time to time. iOS 14.7.1 contains significant security fixes.