Apple has officially closed the signing window for iOS & iPadOS 15.6.1 on Monday after just last week dropping a multi-pronged software update comprised of both iOS & iPadOS 15.7 and the debut iOS 16.0 for the iPhone & iPod touch (iPadOS 16.0 is currently delayed for a while longer).
Apple stops signing iOS 15.6.1 following last week’s newer iOS 15.7 & 16.0 releases