Apple has now stopped signing iOS 15.4, since iOS 15.4.1 was released in the past few days. iOS 15.4.1 was released earlier in March and fixes a few issues, including the battery drain issue which was introduced with iOS 15.4.

iOS 15.4.1 also added support for Universal Control on the iPad, between it and a Mac and the ability for an iPhon to be unlocked while wearing a mask.

Apple has also stopped signing tvOS 15.4 and HomePod OS 15.4.