Why is mute not working correctly on my monitor?

A monitor can support DDC volume adjustments while ignoring or mishandling its separate mute command. Working volume therefore does not guarantee working mute or unmute.

A DDC volume command sets a numeric level, while a mute command requests a muted or unmuted state. Setting volume to its minimum is a different operation and does not guarantee silence on every monitor. Likewise, raising the volume may not release a separate mute state. Some monitors need different mute-on/off values or a particular order of volume and mute commands.

Follow Fix mute and unmute on an external display to choose compatible mute/unmute methods, check minimum-volume behavior and adjust DDC mute values if needed. If only the native keyboard mute key is affected, the tutorial also explains how to leave that key to macOS.