This question was asked almost three years ago, but it's still valid. The Library app is not optimized for Apple CarPlay, meaning it does not show up on the car's display. The app still works, but you have to navigate through it using the phone, and then it will work through the car, including basic controls on the "Now Playing" screen. You cannot use voice or car touch-screen navigation, which would certainly be safer. This has been my experience in my 2017 Mustang. Others may have a different experience.
Cease to be idle; cease to be unclean; cease to find fault one with another; cease to sleep longer than is needful; retire to thy bed early, that ye may not be weary; arise early, that your bodies and your minds may be invigorated
Doctrine & Covenants 88:124