Apple has now shut down the signed status of iOS 15.7 (19H12) firmware, and you can now no longer swipe into these versions of firmware by brushing.
After Apple unsigned iOS 16.0.3 earlier this week, about a week after releasing iOS and iPadOS 16.1 to the public, Apple also unsigned iOS and iPadOS 15.7.7 on Friday after launching iOS and iPadOS 15.7.1. This also means users can no longer downgrade or upgrade to that version using Finder or iTunes.
Apple typically turns off verification for older versions of iOS after a new version is released to encourage users to keep the operating system up to date.
Apple iOS 15.7.1 / iPadOS 15.7.1 was released at the end of October. iOS 15.7.1 is a smaller update, which Apple only says includes important security fixes.
Version 15.7, on the other hand, was released in mid-September, and in addition to fixing security issues in Contacts, Maps, Safari, Safari Extensions, Shortcuts, and WebKit, the iOS 15.7 and iPadOS 15.7 updates also address multiple kernel vulnerabilities.