have you new ubdate for ios 9.3.5 ??

{..I'd offered a reply - to the later duplicate post that's now been pulled - here's that reply..}

Depending on the vintage of an iOS Device, it may not be capable of using

a later newer system software or iOS build version. So it won't be offered in

software update/upgrade from present older system running in the device.

An example of this I'm aware of, is my iPad Mini1.1 16GB (wi-fi) w/ iOS 9.3.x

and this model like several older vintage, cannot use iOS 10.3.x or newer.

Without identifying your iOS device product (sales order / production year)

that's as close a reason to why you cannot get newer, I'd venture to guess.

On which device?