Following the launch of iOS 16.1 on October 24, Apple has stopped signing iOS 16.0.3, the previously available version of iOS that launched on October 10. As iOS 16.0.3 is no longer being signed, it is no longer possible to downgrade to that version of iOS after installing iOS 16.1.
Apple routinely stops signing older versions of software updates after new releases come out in order to encourage customers to keep their operating systems up to date, so it is not unusual that iOS 16.0.3 is no longer being signed.
iOS 16.0.3 was a smaller bug fix update that addressed bugs that were plaguing the iPhone 14 and iPhone 14 Pro models.
The iOS 16.1 update that replaced it is much larger in scale, introducing See source
