In order to prevent downgrading, Apple has stopped signing iOS 18.2.1.

iPhone owners who have upgraded to iOS 18.3 are no longer able to downgrade to the previous version of iOS 18 because Apple stopped signing iOS 18.2.1 today. A week ago, Apple launched iOS 18.3.

After a week or two following the introduction of a new version of iOS, Apple no longer signs the previous version. Because of a server-side software verification check, an unsigned update cannot be installed on an iPhone. Currently, only iOS 18.3 may be downloaded and used on iPhone devices that are compatible with iOS 18.

Apple keeps smartphones updated with the latest security enhancements by prohibiting users from reverting to previous iterations of iOS.

More than 20 security upgrades and a few Apple Intelligence updates were included in the iOS 18.3 release. Updating iOS software is crucial since one of those upgrades fixed a vulnerability that may have been actively exploited on some devices.