When a DisplayLink dock has power and its application is active but a monitor remains blank, Plugable recommends opening DisplayLink Manager's Displays tab. Each connected screen has a toggle that should be On if it is intended for use. The application state and individual display state are separate checks.

If the monitor is not listed or its toggle is already enabled, move on to permissions and physical connections rather than repeating the same setting change. Include both application visibility and macOS Displays visibility in a support report. Those details help locate where the docking video path stops functioning.