Here’s a bit insight of the iOS 12 (pre-) Jailbreaks. I’ve had my 2 iPhones (7 & X) running at iOS 12.1.1/.2 at this early-iOS-12-jailbreak-time (about January 2019) and I was experimenting with some early “Jailbreaks” and developer tools.
So far the app “Badges”, which uses the root access to change files in the system, worked best. With this app (support up to iOS 12.1.2) you can change the color and transparency of the Notification App badges. Even untethered. I also managed to get SSH access with another app.
In February 2019 Pwn20wnd released the unc0ver JB with iOS 12 Cydia support.
See my iOS 12 Jailbreak setup here.
Here are some screenshots of the pre-jailbreak tests: