As of DisplayLink Manager 14.0 release, the Apple Watch unlock feature is enabled by default, and the option has been removed from the user interface.

DisplayLink Manager 1.5 Beta introduced experimental support for Apple Watch unlock with docking stations featuring DisplayLink technology.

You can enable this feature via the DisplayLink Manager app:

Unlocking your MacBook with an Apple Watch is a feature developed by Apple, not by Synaptics.

You can learn how to configure your Apple Watch to unlock your MacBook from Apple Help: "Unlock your Mac with your Apple Watch".

Please note that this feature is not compatible with screensavers. To use Apple Watch unlock with your DisplayLink docking station or graphics adapter, you must disable your screensaver so your monitor goes to sleep/power save mode instead of staying on.