Apple started rolling out the iOS 12.1 update for iPhone and iPad devices on Oct 30th. However, the update is being delivered as iOS 12 for many users. There’s no mention in the Settings app about the update being iOS 12.1 at all. Even the changelog is for the iOS 12.0 update only.
The issue is probably appearing for users who already have the iOS 12.1 beta installed on their iPhone or iPad. Even after removing the beta profile, the software update is shown as iOS 12.
But rest assured, even if the update is showing as iOS 12, you’re getting the iOS 12.1 update instead. It’s a bug/issue on Apple’s side of things that the new update is being mentioned as iOS 12, not iOS 12.1.