https://wccftech.com/apple-stops-signing-ios-13-1-downgrade-no-longer-possible/

Apple had seen fit to release iOS 13.1.2 last week and today, the company stops signing iOS 13.1. What this means is that you can longer downgrade to the build. Apple wants iOS users to stick to the latest version and the only build Apple is signing right now is iOS 13.1.2, which is the latest public release. Let's dive in to see some more details on the subject.

If you're running an older version of iOS, updating to the latest build would mean that you're stuck with it. Since Apple is not signing iOS 13.1 anymore, you can not downgrade to any older versions of iOS 13.  However, Apple is still signing iOS 12.4.2 so if you're not happy with the latest release, you have the option available to go back to the previous version which is bound to be more stable.