If your phone is not jailbroke, Apple CarPlay only allows approved apps to be used which allows you to use the touch screen to control the apps' functions. There are some YouTube videos showing that you can use non-approved apps on CarPlay with jailbroke iPhone and you can reference from there.
If you are talking about screen mirroring, then you will want to get a headunit that supports HDMI input. Then you will need an lightning to HDMI adapter to mirror your phone to your headunit. The bad part about this screen mirroring is that you wont be able to control the phone/app on your headunit.
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