[Android Auto General] G A S T:
At first I want to post what's the given Information from Google and then ask afterwards, what I don’t get here.

Requirements

(pls click here to get to the original Source):

A compatible Android phone with an active data plan, 5 GHz Wi-Fi support, and the latest version of the Android Auto app. Wireless projection is compatible with these Android versions:

Any phone with Android 11.0

A Google or Samsung phone with Android 10.0

A Samsung Galaxy S8, Galaxy S8+, or Note 8, with Android 9.0

A compatible car or stereo. Find out if your car or stereo is compatible with Android Auto .

Tips:

To find out if your phone has 5 GHz Wi-Fi support, contact your manufacturer.

In the EU, to use 5 GHz Wi-Fi in the car, your smartphone must comply with additional regulatory requirements. On Google smartphones, Pixel 3 and newer models comply with this requirement.

To find out if your specific car model is compatible with wireless Android Auto, contact your car manufacturer.

=> What I have:

- Mi 8 with LOS 18.1 / GApps Pico installed

- HU with 5 GHz WiFi and Bluetooth

- AA via USB works flawlessly

- CarPlay via USB and Wireless works flawlessly

- Android Auto V. 7.1.614584-release

- Google Play Services 21.48.15

=> What I want: <=

- working AA WIRELESS 😢

Recommend installation process from Google:

Step 1. Prepare your phone & car​

Make sure your phone meets the minimum requirements.

Confirm that your car is compatible with Android Auto Wireless . If you're not sure, contact your local car dealer.

Ensure your phone has a strong and fast cellular data connection.

Step 2. Connect your phone​

Important: The first time you connect your phone to the car, you’re required to pair your phone and car via Bluetooth. For best results, keep Bluetooth, Wi-Fi, and Location Services turned on during setup. Make sure your car is in park (P) and allow time to set up Android Auto before you start your drive.

Plug a USB cable into your vehicle’s USB port and plug the other end of the cable into your Android phone.

Your phone might ask you to download the Android Auto app or update to the newest version of the app.

Follow the on-screen instructions to complete setup.

Step 3. Start Android Auto​

Your wireless connection might take a few seconds to start. You might need to tap Android Auto on your car display.

Step 4. Disconnect your phone (from wireless projection)​

If you want to stop using Android Auto wirelessly, on your phone notifications screen, tap Exit driving mode.

Drive safely. Pay attention to the road and driving conditions, and always obey applicable laws.

Now my questions:

1.Why does that f***Ing sh*t* installation procedure not work, even if I stick to everything? Any ideas?

2. Can anybody explain me what has (technically) to happen between the AA app on the smartphone and the head unit of my car, so that I can try to force both devices to do what is intended?

3. Why to hell does the AA wireless implementation need a USB cable connection (you see this is somehow connected with question 2)?

4. Are there any special settings (not the standard toggles) in the AA App (or in the AA developer options or the developer options of LOS) which I should (or possibly shouldn't!) have done to make it work?

It would be great, if somebody could help me to unterstand the setup process and my problem in this case.