You may recall that Apple recently started signing iOS & iPadOS 17.3.1 again for unknown reasons after initially unsigning it. In effect, this meant that iPhone and iPad users could downgrade to iOS & iPadOS 17.3.1 from newer firmware again because Apple’s online servers would have provided the green flag necessary to move forward with it.
iOS 17.3.1
Apple unexpectedly once again signing iOS 17.3.1 for many devices, enabling firmware downgrades
In an unexpected turn of events, iOS & iPadOS 17.3.1 appears to be re-signed again despite Apple’s original un-signing of the firmware on March 12th.