You can control music and still navigate while in CarPlay. I do it all the time.

When I first started using CarPlay, the screen that has the music and map showing simultaneously was not obvious and it wasn’t until well into my third long trip with CarPlay that I finally discovered it. I had thought the only display options were app full screen and app list. I think there was a change sometime in the last 3 years that made that the default starting display (or maybe I’m just a little less dumb now).