...Now it has found some other app to show in the left third of the screen which is annoying as it just says "Media Unavailable". I have no idea what the app is. I used to be able to remove it by going into the app drawer and selecting Maps, which would force it to full screen, but it no longer behaves like that.
A setting to say "I never want Android Auto to show a media option" would be awesome. Why would I want to use my phone to play music over data when the car has an excellent radio?
Also, I'd love to be able to not show the Search dropdown by default. Seems invasive to show my passengers things I've previously searched for. I don't really have much to hide, but I spend a second looking away from the road every trip hiding it. Can't be an ideal setup....
The frame on the left of your picture can basically provide a shortcut non full screen way to play the media files from your phone, and for into messaging. From what I understand, it's a standard function of Android Auto, not an app.
If you have an Android Auto compatible media player app on your phone (like VLC for example, but I'm pretty sure the frame also works with others), then in the frame there will be controls for selecting and playing the media files from your phone. Lots of folks have a ton of media files on their phones and listen to them in their vehicle, without the need of using phone data for streaming services.
Likewise, if you have an Android Auto compatible messaging and contacts apps on your phone, the frame may periodically display for into a recent message received or sent thread, or a recent contact with whom you've messaged.
For me, the frame is not massively useful and I can still get rid of it by going into full screen mode for any other app (like maps or messages).
I agree that a good radio station is fine. However, most people seem to like the option of having control over listening to the media they want to hear when they want to hear it, as opposed to whatever a radio station decides.
I agree that the search drop down is annoying. If you touch the up drop down arrow, it'll slightly minimize, as I think you've been doing, but I don't think there's a way to complely get rid of it.