Application doesn't build after adding Admob

Question

I'm using Android Studio 3.5.0 and when I finished my application it worked fine with minSdkVersion 16. However, when I added admob code it doesn't build. I kept upgrading till minSdkVersion 26 and com.android.tools.build:gradle:4.0.1 but when the build finishes successfully, the app doesn't open at all. I tried on many smartphones but it's still crashing.

MainActivity.java

package com.example.simou;

import android.annotation.SuppressLint;
import android.app.Application;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.view.View;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.LinearLayout;
import android.widget.ProgressBar;
import androidx.appcompat.app.AppCompatActivity;
import androidx.swiperefreshlayout.widget.SwipeRefreshLayout;

import com.google.android.gms.ads.AdListener;
import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.AdSize;
import com.google.android.gms.ads.AdView;
import com.google.android.gms.ads.LoadAdError;
import com.google.android.gms.ads.MobileAds;
import com.google.android.gms.ads.initialization.InitializationStatus;
import com.google.android.gms.ads.initialization.OnInitializationCompleteListener;


public class MainActivity extends AppCompatActivity {
private WebView webView;
private ProgressBar progressBar;
private SwipeRefreshLayout swipeRefreshLayout;
private LinearLayout NoInternetLayout;
    private AdView mAdView;

    @SuppressLint("SetJavaScriptEnabled")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        MobileAds.initialize(this, new OnInitializationCompleteListener() {
            @Override
            public void onInitializationComplete(InitializationStatus initializationStatus) {
            }
        });

        mAdView  = new AdView(this);

        mAdView.setAdSize(AdSize.BANNER);

        mAdView.setAdUnitId("ca-app-pub-3940256099942544/6300978111");

        mAdView = findViewById(R.id.adView);
        AdRequest adRequest = new AdRequest.Builder().build();
        mAdView.loadAd(adRequest);


        mAdView.setAdListener(new AdListener() {
            @Override
            public void onAdLoaded() {
                // Code to be executed when an ad finishes loading.
            }

            @Override
            public void onAdFailedToLoad(LoadAdError adError) {
                // Code to be executed when an ad request fails.
            }

            @Override
            public void onAdOpened() {
                // Code to be executed when an ad opens an overlay that
                // covers the screen.
            }

            @Override
            public void onAdClicked() {
                // Code to be executed when the user clicks on an ad.
            }

            @Override
            public void onAdClosed() {
                // Code to be executed when the user is about to return
                // to the app after tapping on an ad.
            }
        });

        progressBar = findViewById(R.id.progress_horizontal);
        swipeRefreshLayout = findViewById(R.id.SwipeRefresh);
        NoInternetLayout=findViewById(R.id.NoInternetLayout);

        webView = findViewById(R.id.webView);
        webView.getSettings().setJavaScriptEnabled(true);
        webView.setWebViewClient(new myWebViewClient());
        chekInternet();
        swipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {
                webView.reload();
            }
        });
    }
    @Override
    public void onBackPressed() {
        if(webView.canGoBack()){
            webView.goBack();
        }
    }

    private class myWebViewClient extends WebViewClient {
        @Override
        public void onPageFinished(WebView view, String url) {
            progressBar.setVisibility(View.GONE);
            swipeRefreshLayout.setRefreshing(false);
            super.onPageFinished(view, url);
        }
        public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
            super.onReceivedError(view, errorCode, description, failingUrl);

            NoInternetLayout.setVisibility(View.VISIBLE);

        }
    }


    private void chekInternet(){
        ConnectivityManager connectivityManager= (ConnectivityManager) getApplicationContext().getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo wifi=connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
        NetworkInfo mobile=connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);

        if (wifi.isConnected()){
            webView.loadUrl("https://5edmatunisie.blogspot.com/");
            webView.setVisibility(View.VISIBLE);
            NoInternetLayout.setVisibility(View.INVISIBLE);
        }
        else if (mobile.isConnected()){
            webView.loadUrl("https://5edmatunisie.blogspot.com/");
            webView.setVisibility(View.VISIBLE);
            NoInternetLayout.setVisibility(View.INVISIBLE);
        }
        else {
            webView.setVisibility(View.INVISIBLE);
            NoInternetLayout.setVisibility(View.VISIBLE);
        }
    }

}

AndroidManifest.xml

 ?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="com.example.simou">

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

    <application

        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme"
        tools:ignore="GoogleAppIndexingWarning">
        <activity android:name=".MainActivity">
            <!-- Sample AdMob app ID: ca-app-pub-3940256099942544~3347511713 -->
            <meta-data
                android:name="com.google.android.gms.ads.APPLICATION_ID"
                android:value="ca-app-pub-3940256099942544~3347511713"/>
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>

        </activity>

    </application>

</manifest>

build.gradle

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        google()
        mavenCentral()
        jcenter()
        
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:4.0.1'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        mavenCentral()
        jcenter()
        
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

build.gradle module

apply plugin: 'com.android.application'

android {
    compileSdkVersion 32
    buildToolsVersion "32.0.0"
    defaultConfig {
        applicationId "com.example.elkhedma"
        minSdkVersion 26
        targetSdkVersion 32
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"

    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'androidx.appcompat:appcompat:1.4.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.2'
    implementation "androidx.swiperefreshlayout:swiperefreshlayout:1.1.0"
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
    implementation 'com.google.android.gms:play-services-ads:20.5.0'

}