MobileAds.initialize(Context, String) is deprecated

Initialize MobileAds with the following instead:

MobileAds.initialize(this, initializationStatus -> { });

Get started with AdMob in your Android project seems to answer the application ID part:

Add your AdMob App ID to your app's AndroidManifest.xml file by adding the <meta-data> tag as shown below.

Important: This step is required as of Google Mobile Ads SDK v17.0.0. If you don't add this <meta-data> tag, your app will crash with the message: "The Google Mobile Ads SDK was initialized incorrectly."

<manifest>
    <application>
        <!-- Sample AdMob App ID: ca-app-pub-3940256099942544~3347511713 -->
        <meta-data
            android:name="com.google.android.gms.ads.APPLICATION_ID"
            android:value="ADMOB_APP_ID"/>
    </application>
</manifest>

And the publisher ID still is required for Requesting Consent from European Users.