I'm afraid I already know the answer to this question, but I need confirmation from the forum's cognoscenti.

WHERE' S THE MUTE BUTTON?

If, as I suspect, there is none, it'll be my first car w/o one since that Model T I bought way back...

 

The volume button. Just push it.

 

Or the power button for the audio system next to the gear selector.

 

This.

It's instant on and off, so a mute button would be of no benefit.