An external monitor connected through a DisplayLink dock may have no brightness slider in Windows Display Settings. Plugable explains that this control is primarily intended for supported built-in displays. The missing slider does not establish that the dock or monitor has malfunctioned.

Use the monitor's buttons or joystick to open its on-screen display and adjust the brightness or picture settings. Some compatible monitors and software can also communicate through DDC/CI, which DisplayLink supports. Availability depends on the complete combination, so the monitor's own controls remain the recommended starting point.