You can enable this feature via the DisplayLink Manager app:
- Click DisplayLink Manager icon in the menu bar
- Enable option "Use Apple Watch to unlock on login screen"
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.