iOS 15.4 is no longer supported by Apple in favor of iOS 15.4.1
As expected, Apple has stopped signing iOS 15.4, meaning that this version of iOS is no longer being supported by Apple and users cannot downgrade to it once they’ve installed the latest iOS update, which, at the current time is iOS 15.4.1, released on March 31, 2022.
Ceasing the support for earlier iOS versions is common practice for Apple, which is aimed at encouraging users to update their devices to the latest version of the iOS. Installing such updates is important as they often fix important bugs and issues present in earlier versions. Case in point, Apple has stated that the 15.4.1 update fixes an AppleAVD bug that could be exploited by a malicious application, allowing the latter to execute arbitrary code in the device by gaining kernel privileges. According to Apple, this vulnerability may have already been exploited in the wild, which is why it’s important to get the latest iOS version in order to secure your iOS device.
Another fix that comes with 15.4.1 is a fix for the battery drain issue that was reported by some iPhone users whose devices were running on iOS 15.4.
The 15.4 update was a notable one – it introduced support for unlocking iPhones while the user is wearing a face mask, added new emojis, and introduced the long-awaited Universal Control feature for iPad. Those were only some of the changes that came with the 15.4 version of iOS. Note that all of these features are also in 15.4.1, so there’s no reason not to update your device.
On a related note, Apple has also ceased its support for HomePod 15.4 and tvOS 15.4 after the recent release of updates for both of them.