Apple has stopped signing iOS 13.4.1 following the release of iOS 13.5. This means if you’re on a higher version of iOS, then you can’t downgrade to iOS 13.4.1 now.
The iOS 13.4.1 software release addressed a FaceTime bug that prevented devices running iOS 13.4 from participating in FaceTime calls with devices running iOS 9.3.6 and earlier or OS X El Capitan and earlier. It’s now replaced by iOS 13.5, which comes with Exposure Notification API, improved Face ID, and more. In fact, iOS 13.5 was jailbroken just a few days after its release.
Additionally, Apple has also stopped signing iOS 12.4.6 on older devices not eligible for iOS 13. Given there’s already an active jailbreak available for iOS 13.5 on all devices, Apple could soon release a new iOS software update to patch the vulnerability as it usually does.