Following the release of iOS 16.3.1 on February 13, Apple discontinued signing iOS 16.3, the most recent version of iOS. After receiving the iOS 16.3.1 update, it is no longer possible to perform a downgrade to iOS 16.3 because Apple has stopped signing that version of iOS.
Apple discontinues the signing of previous versions of iOS after the launch of a new release to encourage users to maintain the most recent version of their operating systems. As a result, the update for iOS 16.3 is no longer being signed.
iOS 16.3 was a minor update that included support for physical security keys for Apple IDs, expanded Enhanced Data Protection globally, added support for the second-generation HomePod, and added support for many other products.
Apple published the first beta of iOS 16.4 last week, adding support for new emoji types, online push notifications, and many other features. The iOS 16.3.1 operating system version is still the most recent version available to the general public.