Apple has stopped signing iOS 13.3.1 after the release of iOS 13.4, stopping people who have upgraded to the latest version from going back again.
Every iOS update Apple introduces is designed to be speedier, more stable, and more secure than its predecessor. As a result, Apple blocks downgrades soon after its latest release has rolled out to everyone. This was the turn of iOS 13.3.1 to go to the big software graveyard in the sky!
iOS and iPadOS 13.4 rolled out on March 24. The big new iOS feature was iCloud Drive folder sharing, designed to make it easier to collaborate with friends or co-workers. (Perfect in this working from home, a.k.a. WFH, times!)
There was also a rearranged toolbar for the Mail app, making the delete icon harder to hit accidentally. Finally, the update included new Memoji stickers. These featured the likes of Party Horn, Rolling Eyes, and Person Behind a Computer. iPadOS 13.4, meanwhile, added robust mouse and trackpad support.
Apple stopped signing iOS 13.3.1 late Tuesday. That was just after Apple released the first surprise beta builds for iOS 13.4.5, iPadOS 13.4.5, macOS 10.15.5 and tvOS 13.4.5 for developers. Those updates predominantly focus on bug fixes.