Install iOS 9 on iPhone 6 with iOS 11

[barbu110]

Hi!

I bought an iPhone 6 last year with iOS 9 installed. I have recently upgraded to iOS 11 (prior to that, I had upgraded to iOS 10) so restoring my phone to the last update via iTunes is not an option now.

Does Apple officially support installing iOS 9 on my iPhone again? (e.g. from this source)

If i install iOS 9 from that source will I be able to restore the backup I made on iOS 11 (photos, contacts, apps)?

Thank you very much!

EDIT
The backup is stored in iCloud

 

[cwwilson]

I’m just gonna give you the short answer here: No.

 

[barbu110]

I’m just gonna give you the short answer here: No.

What will I lose?
I could copy the photos & videos via iTunes in my computer. What else is there in the backup?

 

[eyoungren]

Hi!

I bought an iPhone 6 last year with iOS 9 installed. I have recently upgraded to iOS 11 (prior to that, I had upgraded to iOS 10) so restoring my phone to the last update via iTunes is not an option now.

Does Apple officially support installing iOS 9 on my iPhone again? (e.g. from this source)

If i install iOS 9 from that source will I be able to restore the backup I made on iOS 11 (photos, contacts, apps)?

Thank you very much!

EDIT
The backup is stored in iCloud

I will give the long answer. No you cannot downgrade.

Apple does not allow downgrades and any site saying you can is fake.

Apple digitally signs it's firmware which allows it to be installed. Your phone checks in either OTA or through iTunes when attempting to install 'X' firmware and if Apple is not sigining that firmware the install is not allowed to proceed.

Apple stopped signing iOS 9 over a year ago. You can go to that site and download all the IPSWs you want, you cannot install them.

PS. Not even a jailbreak will help you here as there is currently no way to downgrade a 64-bit device, even when jailbroken. If there was, you'd probably need SHSH blobs and if you don't know what those are then you won't understand the process.

 

[roland.g]

No you cannot install iOS 9 on your phone in any way as you did not do any of the steps to be able to downgrade it which would have required quite some work. The only reason I suspect you want to do this is to then jailbreak it as there are many more functional JB tweaks and mods for iOS 9 than for iOS 10. Even if iOS 11 sees an eventual JB, most of the good devs have left and are not updating mods with compatibility beyond iOS 9. So unfortunately you cannot get the advances of iOS 10 or 11 and still retain the additional functionality of the plethora of iOS 9 tweaks.