The unc0ver jailbreak has been updated with support for jailbreak A12 iPhones on iOS 12.4.1. The release of unc0ver v3.8.0 b1 was announced on Twitter today by Pwn20wnd.
● Add iOS 12.4.1 support for A12 iPhones (iPads not supported at this time)
You can find instructions on how to jailbreak your device using unc0ver here:
● How to Jailbreak Your iPhone Using Unc0ver (Mac)
● How to Jailbreak Your iPhone Using Unc0ver (Windows)