How do I silence Siri on my HomePod mini?

By default, Siri on HomePod mini comes enabled and very loud, and the minimum volume (as far as I can tell) is irritatingly loud. In fact, the whole talkback from Siri (confirming commands, etc.) is irritating and unnecessary. But I can’t find how to simply shut off talkback (as I can with Siri on my iPhone).

How do I silence Siri’s talkback on my HomePod mini?