Apple will allow you to uninstall the security updates deployed through iOS 16’s Rapid Security Response mechanism, which may apply fixes without requiring you to upgrade your iPhone completely (or even without having to restart it, in some cases). According to a MacRumors support post, you may uninstall a Rapid Security Response update by heading to Settings > General > About, then pressing on the iOS Version. You’ll then be given the option to “Remove Security Update.”
The guide provides no examples of why you would need to remove one of the updates, potentially leaving your phone vulnerable to the vulnerability it safeguards against. It’s simple to envisage a few unique situations in which the capability may be valuable, such as if one accidentally corrupts some important work-related software or management tools. Otherwise, it’s one of those things that, unless they have a very special reason and completely understand what they’re doing, most people should definitely never use — similar to the new severe Lockdown Mode, which is included to defend users from “very sophisticated” targeted cyberattacks.
Rapid Security Response is enabled by default, but you can disable it by navigating to Settings > General > Software Update > Automatic Updates and switching off “Security Responses and System Files.” You’ll have to wait for complete iOS upgrades to acquire the security fixes if you do. Again, I’d advise against disabling the functionality unless you have a specific need to do so, considering how many of Apple’s recent upgrades have addressed really major issues.
The system is also coming to macOS in Ventura, which has yet to be formally published — so yet, Apple’s support manuals for its desktop OS make no indication of whether you’ll be able to roll back those upgrades as well.