Apple has stopped signing iOS 11.4.1 which means that it is no longer possible to downgrade from iOS 12.
Currently, Apple’s latest firmware is iOS 12.0.1 and developers have been seeded with iOS 12.1. If you accidentally update or restore, you’ll find yourself on iOS 12.0.1.
Those interested in jailbreaking are typically advised to stay on the lowest firmware possible; however, both PanguTeam and Luca Todesco have achieved successful jailbreaks of iOS 12 and the iPhone XS. Unfortunately, there’s no word yet about a possible public release.