1, Make sure that “Show mirroring options in the menu bar when available” is checked in Display preferences.

2, Accept the DisplayLinkUserAgent accessibility dialogue box which opens System Preferences -> Security&Privacy -> Privacy -> Accessibility.

3, Allow DisplayLinkUserAgent application to control your computer.

4, Connect your DisplayLink enabled device.

5, You should now see the Airplay icon in your systems tray.

6, Click "Use as Separate Display" to switch to extended desktop mode.