Apple recently released iOS 15.2, and as is traditional, Apple has now stopped signing iOS 15.1.1 and iOS 15.1, making downgrading to those versions of iOS no longer possible.
Apple last week released iOS 15.2. iOS 15.2 adds Apple Music Voice Plan, a new subscription tier that provides access to music using Siri. This update also includes the App Privacy Report, new safety features for children and parents in Messages, and other features and bug fixes for your iPhone.
The new software can be downloaded on compatible devices over-the-air by going to “Settings” -> “General” -> “Software Update.”
Falling back to an older iOS build is often used by users that jailbreak their iPhones. Restoring an iPhone or iPad to a previous version of iOS can also sometimes be helpful for users who experience significant bugs after upgrading to the latest version of iOS.