When you upgrade an iOS version you can only proceed after an Apple signing server approves that version of iOS for your devices unique hardware identifier. Whe

When you upgrade an iOS version you can only proceed after an Apple signing server approves that version of iOS for your devices unique hardware identifier. When their server stops signing an iOS version everyone is locked out of installing it. In the jailbreaking world you can save these signatures allowing you to install that iOS version later at your leisure. That said, Apple appears to still be signing iOS 14.8. You can check the signing status here: https://ipsw.me/iPhone12,3 https://ipsw.me/iPhone12,3 (But look up your device model in particular. Sometimes there’s inconsistencies)