iOS 15.6.1 no longer being signed
According to Apple, iOS 15.6.1 has fixed two major vulnerabilities that let apps execute arbitrary code without the user’s consent. The update was made available to the public on August 17. But of course, these security fixes (in addition to new ones) are all included with iOS 16, so it’s no surprise that Apple has stopped supporting iOS 15.6.1.
Reverting to older iOS builds is often used by those who jailbreak their iPhones and iPads. Earlier this month, the Odyssey Team group announced that they’ve been working on the first jailbreak tool for devices running iOS 15. However, due to how strong the system protections have become, this tool will only work with versions from iOS 15.0 to iOS 15.1.1.
Restoring an Apple device 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.
There’s still a way to downgrade from iOS 16
While you can’t easily revert to iOS 15.6.1 or even iOS 15.1, you still have a chance to downgrade from iOS 16 to a more recent version of iOS 15. That’s because Apple last week released iOS 15.7, which brings security fixes for users who don’t want to install iOS 16 yet.