Volume is very low when using maps/navigation in CarPlay

Yes, try it. It has worked in my car. It's like the music has one volume, voice and navigation have another, and calls have a third volume.

Ask Siri to tell a joke to make her talk longer. While she is talking, you set the volume by turning up the volume in the car on the steering wheel, or via the car stereo, and again, remember your iPhone must be connected to CarPlay when you do it.

Try this. Siri and Navigation Voice are connected. Activate Siri when connected to CarPlay. When she answers again, you turn up the volume for a suitable volume. Subsequently, the navigation voice should have the same volume.