How to solve the no audio output from a BenQ monitor's built-in speaker?

1.  Check the specification of your monitor and find out whether it comes with
     a built-in speaker.

2.  Make sure to plug and connect the correct port on the monitor.

• If the headphone or external speaker is connected to your monitor, try to remove it.
• When using HDMI, DisplayPort, or USB-C as the output source, audio
  is transmitted via the same cable alongside video.

3.  Check the sound settings on your computer (Windows/Mac)

• Windows:
  1. Go to Windows settings, select System, then click the sound option.
      Choose the output device from the monitor, then adjust the volume.
  2. When you cannot find your monitor on the output device list, unplug and
      replug the cable. 

• Mac:

    1. Go to Mac settings,  then click the Sound option. Choose the output
        device from the monitor, then adjust the volume.
    2. When you cannot find your monitor on the output device list, unplug and
        replug the cable.

4. Check the volume settings of your monitor

    Menu > Audio > Speaker

For more detail, refer to the video link: