With the release of iOS 12.1.2 earlier this week, Apple has officially stopped signing iOS 12.1. What this means is that downgrades to the .1 version are no longer available with the minimum downgrade option is to version 12.1.1. For most consumers, this will have little impact but it is worthy to note in case you are not happy with the latest version.
The process of “signing” essentially means that Apple takes the build away as an option on their update servers. This is a normal process that the Cupertino company has when new builds of iOS are offered up. The reason is so that Apple can keep customers on the most current version, thus lowering support versions of iOS.
Version 12.1.2 brought several bug fixes and improvements to iPhones earlier this week. Most of those fixes had to do with the eSIM built into the iPhone XS lineup and the iPhone XR. eSIM support originally rolled out with 12.1.1 a few weeks back.
If you are running iOS 12.1 and want to stay on it, there is no requirement that you upgrade to version 12.1.1 or 12.1.2. This is not going to force you to upgrade your iPhone or your iPad. What it does mean is that if you upgraded to .1.1 or 1.2, you won’t be able to go back to 12.1 if you wanted to do so.