You can download iOS 16.0 & iPadOS 16.0 IPSW firmware files for all devices from this page. This firmware file can be restored with iTunes if and only if it is still being signed by the time you download it. Note that our website provides firmware directly from Apple's server using the ipsw. me API.
IPSW, iPhone Software, is a file format used to install iOS, iPadOS, tvOS, HomePod, and most recently, macOS firmware for devices equipped with Apple silicon.