Were you looking forward to the iOS 11.3.1 jailbreak? Well, it's too late now if you've already updated to iOS 11.4 as Apple has stopped signing iOS 11.3.1.
Apple Stops Signing iOS 11.3.1 - Downgrade and Jailbreak no Longer Possible
Ever since the release of iOS 11.4, it was only a matter of time Apple would stop signing iOS 11.3.1, making the former version the go-to software for all users around the globe with a supported device. This also means that if you were hoping to downgrade to iOS 11.3.1 in order to jailbreak your device using the recently updated tool Houdini, then you can no longer do that as well.
This news is good and bad at the same time. Bad since you can no longer jailbreak obviously, and good as iOS 11.4 brings excellent two features to everyone - Messages in iCloud and AirPlay 2. The former lets you sync all your Messages threads across devices while the latter allows you to play audio from multiple speakers, something which wasn't possible before using AirPlay.
If you are wondering whether or not there's a way to downgrade to iOS 11.3.1, then I will gladly go ahead and crush your hopes and dreams as there isn't any. If you download the firmware onto your PC or Mac right now and try to restore your device using iTunes, the process will simply fail since Apple is not signing the firmware.
You may like to check out: