Apple today stopped signing iOS 17.3, preventing iPhone users from downgrading to that version of iOS. iOS 17.3 is no longer being signed following the February 8 release of iOS 17.3.1, an update that added a fix for a text-related bug.
Apple routinely stops signing older versions of iOS, so it is not unusual that the iOS 17.3 update is no longer available. Apple prevents users from installing older versions of iOS to encourage customers to keep their operating systems up to date and to prevent downgrading to older, less secure versions of the iPhone operating system.
iOS 17.3.1 is now the only publicly released version of iOS available, but Apple is also beta testing iOS 17.4. Both developers and public beta testers can download and install iOS 17.4, with the update adding a number of App Store-related changes in the EU, new emoji, transcripts in the Podcasts app, and more.
Article Link: Apple Stops Signing iOS 17.3, Downgrading No Longer Available