Android Studio 3.6.1 | Error: "This project uses AndroidX dependencies" [duplicate]

I have updated my Android Studio and the targetSdkVersion (build.gradle) to 29. I migrated to AndroidX. Now the Gradle build gives me these 2 errors.

This project uses AndroidX dependencies, but the 'android.useAndroidX' property is not enabled. Set this property to true in the gradle.properties file and retry.

The following AndroidX dependencies are detected: androidx.versionedparcelable:versionedparcelable:1.0.0, androidx.fragment:fragment:1.0.0, androidx.slidingpanelayout:slidingpanelayout:1.0.0, androidx.core:core:1.0.0, androidx.customview:customview:1.0.0, androidx.swiperefreshlayout:swiperefreshlayout:1.0.0, androidx.interpolator:interpolator:1.0.0, androidx.loader:loader:1.0.0, androidx.drawerlayout:drawerlayout:1.0.0, androidx.viewpager:viewpager:1.0.0, androidx.collection:collection:1.0.0, androidx.localbroadcastmanager:localbroadcastmanager:1.0.0, androidx.lifecycle:lifecycle-common:2.0.0, androidx.arch.core:core-common:2.0.0, androidx.annotation:annotation:1.1.0, androidx.lifecycle:lifecycle-livedata:2.0.0, androidx.legacy:legacy-support-core-ui:1.0.0, androidx.lifecycle:lifecycle-viewmodel:2.0.0, androidx.lifecycle:lifecycle-livedata-core:2.0.0, androidx.arch.core:core-runtime:2.0.0, androidx.legacy:legacy-support-core-utils:1.0.0, androidx.documentfile:documentfile:1.0.0, androidx.cursoradapter:cursoradapter:1.0.0, androidx.lifecycle:lifecycle-runtime:2.0.0, androidx.coordinatorlayout:coordinatorlayout:1.0.0, androidx.asynclayoutinflater:asynclayoutinflater:1.0.0, androidx.print:print:1.0.0

My code is: MainActivity.java

package it.manuel.myapp;

import android.Manifest;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.DownloadManager;
import android.app.Notification;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.content.DialogInterface;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.os.Build;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.webkit.DownloadListener;
import android.webkit.URLUtil;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.iid.FirebaseInstanceId;
import com.google.firebase.iid.InstanceIdResult;
import com.google.firebase.messaging.FirebaseMessaging;


public class MainActivity extends AppCompatActivity {

    private WebView webView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        webView = (WebView) findViewById(R.id.webview);
        webView.setWebViewClient(new WebViewClient());
        webView.loadUrl("http://google.com/");
        WebSettings webSettings = webView.getSettings();
        webSettings.setJavaScriptEnabled(true);

    }




    @Override

    public void onBackPressed() {
        if (webView.canGoBack()){
            webView.goBack();
        } else {
            super.onBackPressed();
        }
    }
}

build.gradle

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

buildscript {

    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.6.1'


        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
        classpath 'com.google.gms:google-services:4.2.0'
    }
}

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

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

build.gradle(:app)

apply plugin: 'com.android.application'

android {
    compileSdkVersion 29
    defaultConfig {
        applicationId "it.manuel.myapp"
        minSdkVersion 29
        targetSdkVersion 29
        versionCode 2
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    productFlavors {
    }
    compileOptions {
        sourceCompatibility = 1.8
        targetCompatibility = 1.8
    }
    buildToolsVersion = '28.0.3'
}

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    implementation 'com.google.firebase:firebase-core:17.2.3'
    implementation 'com.google.firebase:firebase-messaging:20.1.1'
    testImplementation 'junit:junit:4.13'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}

apply plugin: 'com.google.gms.google-services'

AndroidManifest.xml

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

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

    <application
        android:allowBackup="true"
        android:usesCleartextTraffic="true"
        android:icon="@mipmap/ic_launcher"
        android:label="MyApp"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

    </application>

</manifest>

I don't understand why it no longer works.

The Android Gradle plugin provides the following global flags that you can set in your gradle.properties file:

android.useAndroidX: When set to true, this flag indicates that you want to start using AndroidX from now on. If the flag is absent, Android Studio behaves as if the flag were set to false.

android.enableJetifier: When set to true, this flag indicates that you want to have tool support (from the Android Gradle plugin) to automatically convert existing third-party libraries as if they were written for AndroidX. If the flag is absent, Android Studio behaves as if the flag were set to false.

To enable jetifier, add those two lines to your gradle.properties file:

android.useAndroidX=true
android.enableJetifier=true