Apple has stopped signing iOS 10.3.3 and iOS 11.0 which means that downgrading or restoring to those firmware versions is no longer possible.
Currently, Apple's latest firmware is iOS 11.0.2 and developers have been seeded with iOS 11.1. If you accidentally update or restore, you'll find yourself on iOS 11.0.2.
As usual, you have a better chance of being able to jailbreak your device whilst on a lower firmware version.
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