https://wccftech.com/apple-no-longer-signing-ios-12-4-1-includes-several-ios-13-versions-too/

The day we were all expecting is here – Apple is no longer signing iOS 12.4.1, iOS 13.1 and iOS 13.1.1.

Whenever Apple is signing a particular firmware version, it means that you can easily downgrade or upgrade to it as long as your device supports it. For example, if you have an iPhone X and wish to downgrade back to iOS 12.4.1, then you can easily do so as long as Apple is signing the latter. But today, Apple dropped the hammer pretty hard and is no longer signing a bunch of previous firmware releases, including iOS 12.4.1, iOS 13.0 and iOS 13.1.1. What’s strange is the fact that the company is still signing iOS 13.1, which is obviously older than iOS 13.1.1 itself. But, if you wish to downgrade to iOS 13.1, you still have the time to do so, and you can do it by skipping iOS 13.1.2 altogether, which was released this week.