iOS 12.1 in the past.
Apple stops issuing digital signature to the iOS 12.1 on the next day after the launch of the final iOS version 12.1.2. This means that iPhone and iPad users is no longer possible to install iOS 12.1 or to revert to the firmware with newer versions.
Once Apple stops issuing digital signature to the iOS 12.1, the company has two current firmware: iOS iOS 12.1.1 and 12.1.2. At the moment, users have to install only these versions of iOS. At the same time, iOS 12.1.2, which was released 18 December, released exclusively for the iPhone version of the firmware for the iPod touch did not.
Apple has released iOS 12.1.2 quite quickly, so it is expected that in the coming weeks the company will launch the following new iOS version. It is not excluded that it will be iOS 12.2 — the long-awaited major update to iOS 12, which will be new features and interface changes.