How do I activate this option?
Open up more options by clicking (...) in the bottom-right corner of the editor.
At the bottom of the pop-up, you'll find the option to Play only audio. Toggle this on to activate the feature.

Open up more options by clicking (...) in the bottom-right corner of the editor.
At the bottom of the pop-up, you'll find the option to Play only audio. Toggle this on to activate the feature.