Following the release of iOS 13.3.1 on January 28, Apple has stopped signing iOS 13.3, which means downgrading to that version of iOS is no longer possible.
iOS 13.3 was a major update that included Communication Limits for Screen Time, support for NFC, USB, and Lightning FIDO2-compliant security keys in Safari, and more.
Apple routinely stops signing older versions of software updates after new releases come out in order to encourage customers to keep their operating systems up to date.
iOS 13.3.1 is the current publicly available version of iOS, with the update introducing a toggle for the U1 Ultra Wideband chip in the newest iPhones along with various bug fixes and improvements.
Developers and public beta testers can also download iOS 13.4, an upcoming update that includes a new toolbar in the Mail app, iCloud Folder Sharing, new Memoji stickers, and more.
This article, “Apple Stops Signing iOS 13.3 Following Release of iOS 13.3.1” first appeared on MacRumors.com