I don't have a pic of the icon options and my car is in the shop (fuel line leak, again), so if you can take a pic and post it, I should be able to tell you which one it is. I think it is like a person speaking or something, not a mic. The instructions may well tell you, too.
So why buy a fancy stereo if you just want to use Android Auto? It is ugly, clunky, and does not do enough IMO. I need to be able to use all my phone's apps on the phone and any app I want on the stereo, plus have a nice-looking screen on the stereo (I use Agama, not the Atoto home screen). I get way more tethered data than I'll ever need included with my phone plan, so that's not an issue for me to use the stereo instead of the phone. I use Google Maps on the stereo (usually using the Atoto mic to tell it where to navigate to but sometimes just using previous places I've looked up since it syncs with what I've looked at on other devices), Bluetooth music from my phone, have Bixby read out loud all my texts and other notifications when they happen (sometimes it is funny when she gets to an emoji), can use Google Assistant (via the phone-mapped button) to respond to texts (although in the car it doesn't get my words correct most of the time - I'm guessing it uses the phone's mic instead of the Atoto's mic? Calls work perfectly/people can hear me fine), and when parked/waiting can use any app.
I don't know if your phone needs to get permissions to use it maybe? I use it as the Bluetooth to my phone's Google Assistant, and last set it up over a year ago when I got my current phone, so I don't remember if it needed permissions or not.
