While Apple stopped signing iOS 12.1.2 quite a few weeks back, it continued signing iOS 12.1.1 beta 3 thereby allowing users running iOS 12.1.3 – iOS 12.1.4 to downgrade back to it and jailbreak their iPhone or iPad. Sadly, that option is no longer available now as Apple has stopped signing iOS 12.1.1 beta 3.
Some users are reporting that they were still able to downgrade their iPhone to iOS 12.1.1 beta 3 so you might want to try your luck. The chances of success are pretty slim though.
Now that Apple has stopped signing iOS 12.1.1 beta 3, it means that if you did not already downgrade your iPhone to iOS 12.1.1 beta 3 or if it is not already running iOS 12.1.1 – iOS 12.1.2, there’s no way you can jailbreak it using Unc0ver. If for some reason you could not downgrade your iPhone to iOS 12.1.1 beta 3, you are out of luck now.
Your only option now is to stick to iOS 12.1.4 on your iPhone and hope that an exploit is discovered sooner than later for it that paves the way for a potential jailbreak. But even then, that is unlikely to happen anytime soon so be prepared for a long wait.
If your iPhone is running any iOS 12 version lower than iOS 12.1.3 and you are interested in the jailbreaking scene, you should immediately save the SHSH blobs as that would allow you to manually downgrade back to that iOS version later on.
Did you miss downgrading your iPhone or iPad to iOS 12.1.1 beta 3?