There are two lock options from what I can tell. One is an actual lock that secures the tailgate from being removed from the vehicle.
The other is a 'remote lock' that operates a lock built into the tailgate, preventing the handle alone from opening the tailgate. IOW, it must be unlocked remotely, or with a key, when it has been previously locked before you can open the tailgate. I assume it should prevent someone from removing the tailgate if locked. Ford has for decades made the tailgate easy to remove by positioning it at an angle such that the right hand pivot/hinge point are angled to release. Open, drop down to about 45 degrees, and lift the right end free.
Others may know better or describe better.