Here is how to mute/unmute a track:

1) To mute/unmute a track, click on the volume button at the beginning of the track.

Here is how to mute/unmute a clip:

1) To mute/unmute a clip, click on the three dots next to the clip's name and select Mute/Unmute from the drop-down menu.

2) Or you can select the Mute cursor from the bottom toolbar and click on the clips you want to Mute/Unmute.