Currently, Apple's latest firmware is iOS 15.7 or iOS 16, and iOS 16.0.1 for the iPhone 14. If you accidentally update or restore, you'll find yourself on one of those versions. For now, it is still possible to manually downgrade from iOS 16 to iOS 15.7. Developers have been seeded with iOS 16.1 beta.
Those interested in jailbreaking are typically advised to stay on the lowest firmware possible. The checkra1n jailbreak makes it possible to jailbreak most devices between the iPhone 5s and iPhone X on any firmware version above iOS 12.3; however, an iOS 15 update has yet to be released. The unc0ver jailbreak and Taurine jailbreak support all devices running iOS 14 - 14.3. Unc0ver has also been updated with the Fugu14 untether which supports iOS 14.3 - iOS 14.5.1. Recently, CoolStar announced that the Odyssey Team will release a new 'Cheyote' jailbreak for devices with an A11 - A14 chip, running iOS 15. Unfortunately, this could be the last jailbreak'.
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