Android Auto now has more stringent requirements

The Android Auto car app is now only compatible with relatively new versions of the Android operating system. From support page For the app, it appears that from now on you will need Android 8.0 (Oreo) or later to be able to use the app and its associated functions. Until recently, this was still Android 6.0 (Marshmallow), as it describes android world.

Android Auto is a feature of Android that allows users to connect their smartphone directly to the car screen. After all, many modern cars have an interactive display in the dashboard. With Android Auto, (car) apps appear directly on the screen and Google Assistant is supported in this way as well. All Android devices running their own OS from version 8.0 are compatible. Google reports here Supported cars.

Smartphones running Android 10 or later have an added advantage. These devices have all the functionality of Android Auto baked into the main operating system. So a separate Android Auto app is no longer necessary for newer versions of Android; These devices can directly connect to supported vehicles.

Sources:
googleAnd the via AndroidWorld