There are semi-unbound jailbreaks, as evidenced by the Electra method of iOS 11, Chimera for iOS 12 and even the new bootrom-based Checkra1n tool for iOS 13. Although not as useful as completely unbound, re-enabling A semi-unbound jailbreak is still fairly easy once you get used to the steps involved.
The biggest handicap of a semi-unbound jailbreak is the need to manually start it when your phone turns off or restarts. Fortunately, power cycling only disables the jailbreak and associated mods instead of being completely removed. Since the jailbreak is only sleeping in the operating system of your iPhone, you just have to reactivate it to get all your tweaks going again.
Step 1: Connect your iPhone & Run Checkra1n
Checkra1n requires that you connect your iPhone to your computer to reactivate your jailbreak, so open the jailbreak tool on your Mac and connect your iPhone with a USB to Lightning cable or a USB-C to Lightning cable. Wait until Checkra1n has read your device and click on "Start" once the connection has been established.
Checkra1n will ask you to start your iPhone in DFU mode. But before this is done, the tool will automatically restart your iPhone, so wait a moment or two until your device enters recovery mode.
Step 2: Go to DFU mode & re-enable Jailbreak
After starting up in recovery mode, Checkra1n gives you instructions on the screen to get you help to enter DFU mode. However, you can also enter DFU yourself if you know what to do – Checkra1n will automatically detect your device as soon as it enters DFU mode and automatically re-enable your jailbreak.