That means you can easily downgrade iPhone 6S to iOS 10.3.3. It’s unknown why Apple sign in the iOS 10.3.3 only for iPhone 6S because Apple has stopped signing iOS 10.3.3 for all devices just a days earlier.
So, if you have missed downgrading your iPhone 6S to iOS 10.3.3, not much enjoying iOS 11/11.0.1/11.0.2, and waiting for Jailbreak then this will be the right time to get back to previous iOS 10.3.3 version.
Other 64-bit devices except iPhone 6S cannot able to downgrade to iOS 10.3.3 and will forced to install iOS 11.0.2.
Since Apple is still signing iOS 10.3.3 firmware, so iPhone 6S users with iOS 11 have an option to downgrade to iOS 10.3.3 as well. No worries! if you had accidentally upgraded iOS 11 through OTA update, you can easily downgrade to iOS 10.3.3 on your iPhone and iPad for some day.
If you feel iOS 10.3.3 is better than iOS 11 or if you have also faced a number of issues on iOS 11, this is the right time to get back to iOS 10.3.3 quickly.
You can check the signing IPSW firmware on https://ipsw.me.
Here’s simple step by step guide to downgrade your iPhone 6S to iOS 10.3.3 from iOS 11.
How to Downgrade iPhone 6S to iOS 10.3.3
First of all, you need to download the iOS 10.3.3 firmware file for your device from our Download page.
Step 1# You need to upgrade or download iTunes to the latest version on your Mac or PC.
Step 2# Now Turn off Find my iPhone & disable passcode lock via the Settings app. (Settings > iCloud > Find my iPhone).
Step 3# Launch iTunes & connect your iPhone, iPad & iPod Touch using data cable to your computer.
Step 4# Hold the Alt/Option key on the Mac or Shift Key in Windows on your keyboard.
Step 5# Now Select the iOS 10.3.3 ipsw file you had downloaded earlier
Step 6# Then click on the Restore iPhone.
Step 7# iTunes will inform that it will restore your iOS device to iOS 10.3.3 and Click Restore
After restored, your device will reboot to the welcome screen and will now install iOS 10.3.3 on your iPhone 6S.
That’s it. Your iPhone 6S is successfully downgraded to iOS 10.3.3 from iOS 11. Set up your device by following the on-screen instructions.