To make the unofficial transition, however, you’ll still need the SHSH blob for the unsigned firmware and for your device.

Restoring to an unsigned iOS version can only be done through unofficial means, such as the use of third-party tools like FutureRestore. Simply put, you can’t restore an unsigned iOS version with iTunes. If one of the firmware is no longer signed, meaning Apple has removed its signature, the downgrade process will fail. If you want to move between two iOS versions, Apple with the help of iTunes will look for this piece of code (SHSH blob) to determine if you’re switching between signed iOS firmware. They also make up a critical part of the iOS Apple signing system. Once installed, any iOS firmware carries a piece of code (or digital signature) many users refer to as SHSH blob. It's not possible to move back to an unsigned iOS without an SHSH blob. Is It Possible to Downgrade to Unsigned iOS without SHSH Blobs? How Do I Revert Back to iOS 13 from iOS 14 without A Computer?

What Does It Mean If IPSW File Is Not Signed Anymore? Is There A Way to Downgrade to an Unsigned iOS Version? Part 3: How to Downgrade iOS with WooTechy iMaster Part 2: How to Downgrade to Unsigned iOS with SHSH Blobs

Part 1: Is it Possible to Downgrade to Unsigned iOS without SHSH Blobs?

Iphone restore firmware