Apple released iOS 16.1.2 on November 30th. And it disabled downloads to previous versions, iOS 16.1 and iOS 16.1.1, so users who upgraded won’t be able to go back.
Disabling Downgrade to Previous Version It is common for Apple to keep their users updated to the latest version of their operating system for security and feature updates. This latest version adds iCloud Photo Library and Live Activities and fixes some bugs.
As for iOS 16.1.2, it is expected to be replaced with iOS 16.2 soon, which is currently in the RC version for developers. And introduced new advanced data protection features for iCloud, Freeform apps, Apple Music Sing and more
source : macrumors