Apple officially stopped signing iOS and iPadOS 13.3.1 Tuesday evening, just one week after releasing iOS and iPadOS 13.4 to the general public as an over-the-air software update.
The closing of the signing window means those who’ve upgraded to the newer 13.4 firmware will be unable to downgrade to 13.3.1. This isn’t a big deal for most iPhone or iPad users, but it’s something that can be particularly unsettling for the jailbreak community as software updates frequently patch jailbreak-centric software exploits.