When sending or receiving messages, the popup no longer occupies the whole screen. It'll now only display a box in the middle.
Interesting. One of my least favorite things about CarPlay is when I'm trying to scroll a list, and a banner appears at the bottom. The banner blocks my scroll gesture, and if I touch it to try to dismiss it or anything, I'm taken out of my current app.
The only thing you can do about it is to just wait for it to go away, which is not good for someone in a car.