Following iOS 16.3 on January 23, Apple stopped signing iOS 16.2, the previous version of iOS. After installing the iOS 16.3 update, it is no longer possible to downgrade to iOS 16.2 since Apple has ceased signing it.
Apple typically removes signing older versions of iOS following new releases in order to encourage users to keep their operating systems up to date, so the iOS 16.2 change is not unusual.
iOS 16.2 was a major update that included Apple Music Sing, the Freeform app, Advanced Data Protection for iCloud, and other features. iOS 16.3 provides support for the new HomePod model, Security Keys for Apple ID, and updates to Emergency SOS.
Apple is expected to release the first beta of iOS 16.4 soon, however, for the time being, iOS 16.3 is the sole version of iOS 16. Following the release of iOS 15.7.3 and iOS 12.5.7 security patches earlier in January, Apple has also ceased signing iOS 15.7.2 and iOS 12.5.6.