Wipe & restore as new from older iOS backup??

[now i see it]

If an iPhone is running iOS 9.3.5 and does a OTA backup, can the phone then be wiped (factory reset) and a fresh copy of iOS 9.3.5 be reinstalled from the backup? OTA ? Via iTunes?

Or once the iPhone is reset, can it only install the latest OS (which soon will be iOS 11)?

My iphone (iOS 9.3.5) is currently running great. I am just curious how it works if it ran into any trouble in the future and had to restore it... cuz I don't want to install iOS 11 on it.
Thanks.

 

[Paddle1]

If an iPhone is running iOS 9.3.5 and does a OTA backup, can the phone then be wiped (factory reset) and a fresh copy of iOS 9.3.5 be reinstalled from the backup? OTA ? Via iTunes?

Or once the iPhone is reset, can it only install the latest OS (which soon will be iOS 11)?

My iphone (iOS 9.3.5) is currently running great. I am just curious how it works if it ran into any trouble in the future and had to restore it... cuz I don't want to install iOS 11 on it.
Thanks.

The Settings app can reset the device without updating.

Backups do not backup the OS itself, only the user data. It'll try to restore to whichever version is on the device.