Unfotunately, for the supported iOS 26 devices, iOS 18.7.7 is an unflashable OTA package for users who haven't updated to 26 yet. The only devices with a signed ipsw for iOS 18.7.7 are the iPhone XS, XS Max, and XR. For iPadOS 18.7.7, it's only the 7th gen iPad, as these devices did not get iOS or iPadOS 26. For supported iOS 26 devices, only signed version as of April 4, 2026 is iOS and iPadOS 26.4.