As for iOS 15.3.1, it was released to users on February 10 with a fix for a security exploit found in WebKit, the engine behind Safari. The update also fixed an issue that may cause Braille displays to stop responding. Reverting to older iOS builds is often used by those who jailbreak their iPhones. Restoring an iPhone or iPad to a previous version of iOS can also sometimes be helpful for users who experience significant bugs after upgrading to the latest version of iOS.
Apple ceased signing iOS 15.3.1 for all iPhone, iPod touch, and iPad models on Wednesday, following the release of iOS 15.4 last week. Users will no longer be able to restore their devices to iOS 15.3.1. On March 14, Apple released iOS 15.4 with a slew of new features, including Face ID unlocking while wearing a mask, Universal Control for iPads, new emojis, iCloud Keychain improvements, and more. The update now includes a new Siri voice for US users as well as Tap to Pay, which turns the iPhone into a contactless credit and debit card payment terminal.
If you have experienced any serious issues with iOS 15.3.1, unfortunately, you’ll now have to wait until a future update rather than downgrading to iOS 15.3. Users running the iOS 15.4 beta can no longer downgrade to iOS 15.3 either.