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

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