Dec 14/2022: Google released the Android Auto Coolwalk update for more users.
Dec 07/2022: Google is releasing a new app update for Google Android Auto that adds several new features and improvements. This update improves the Do Not Disturb functionality and addresses bug-related issues. Additionally, on the car UI, you can now control the Dark Mode from your phone.
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The new Coolwalk interface was officially made available with Android Auto 8.5. at least in theory. Android Auto 8.5, virtually no users have access to the new design.
Android Auto will be made more dynamic and easy to use by the new user interface. For quick access to media recommendations and frequently used apps, select cards can be zoomed in and out.
Additionally, it ought to be easier to read on displays of various sizes and orientations.
However, it would appear that only a few users can take advantage of the new interface. Some other users also have Android Auto 8.5 but no Coolwalk.