Probably the coolest feature, IMO, in CarPlay under iOS 13 is the fact that you can use your phone AND CarPlay simultaneously and independently ... and what is on one screen is no longer mirrored on the other. In the iterations of CarPlay in iOS 12 and prior, the connected iPhone had to display the same app ... Whether Messages, Music, Maps, etc. Now, you can continue to view the navigation screen on CarPlay and check email or messages on your phone without impacting the navigation display. Of course, you should only check your messages or mail on your phone while stopped at a traffic light, etc.
I was very interested in this. It's frustrating that when you get a call that it takes over the screen from your maps application.