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Just got a 2020 a week ago. Took it out for a long drive and had plenty my of screen time. I had the same issues as you did.
Here’s what fixed it. You have to wait a few minutes after starting the car before plugging in the USB cable. I think the Sync OS is still loading drivers/services that allow Apple play to work.
I had 100% success by giving it a few more minutes before using the cable.