The process of reverting an iPhone or iPad to a previous operating system version after an update can be complex and potentially risky. It typically involves downgrading from the latest iOS release to an older version that is still signed by Apple. An example of this would be reverting from iOS 17 back to iOS 16.
The ability to revert to a previous version offers some users the benefit of improved performance on older devices that may struggle with newer operating systems. Occasionally, users might need to revert to a previous version because of unresolved bugs or incompatibility issues with specific apps or hardware. Historically, Apple has made downgrading increasingly difficult as a security measure, primarily to prevent users from running software with known vulnerabilities.