After the official release of iOS 12.4.1 at the end of August. Apple stopped verifying iOS 12.4 today, which means users can no longer downgrade to iOS 12.4.
On July 23 this year, Apple officially released the official version of iOS 12.4. Which brings the iPhone migration function, which can directly transfer data from the old iPhone to the new iPhone. And improve the security of the iPhone and iPad.
On August 20 this year, a hacker named Pwn20wnd released the iPhone’s new public jailbreak tool. The report said that due to iOS 12.4, Apple unexpectedly re-created the vulnerability originally fixed in iOS 12.3. Which opened the door for iOS 12.4.
Since then, iOS 12.4.1 has been officially pushed only one week later and has blocked the jailbreak vulnerability. Apple also thanked the jailbreak developers for their discovery.
For some users who have updated to the latest iOS system. The way to downgrade is sometimes very effective when they encounter major bugs. This is why Apple waits weeks before shutting down the old iOS system verification channel.