Don't Install iOS 12.4.2 If You Jailbreak
If your device is jailbroken or you think you might want to jailbreak your device, avoid iOS 12.4.2.
The iOS 12.4.1 update's sole purpose was to plug up a vulnerability that was used by jailbreak developers to exploit iOS 12.4. Again, iOS 12.4.1's patch is included in iOS 12.4.2.
There is currently no way to jailbreak a device running iOS 12.4.2 or iOS 12.4.1. So, if you're interested in jailbreaking, stick around on iOS 12.4 or an older version of iOS 12.
Jailbreak developers recently released a working jailbreak tool for iOS 12.4, but it doesn't work with newer iPhone models.
If you want to jailbreak an iPhone XR, iPhone XS, or iPhone XS Max, you need to be on an older version of iOS 12. Unfortunately, there's no way to downgrade to older versions of iOS 12.