java.lang.Exception NullPointerException: Attempt to call the virtual method void by reference to a null object

I know this is a very common mistake, but still, please help me find what I missed.
my main activity including the webview element, after adding which an error occurs -

   class MainActivity : AppCompatActivity() {
    @SuppressLint("MissingInflatedId")
    private lateinit var appBarConfiguration: AppBarConfiguration
    private lateinit var binding: ActivityMainBinding
    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val webview = findViewById<WebView>(R.id.webview)
        webview.loadUrl("file:///android_asset/index.html")

        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        setSupportActionBar(binding.appBarMain.toolbar)

        binding.appBarMain.fab.setOnClickListener { view ->
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                .setAction("Action", null).show()
        }
        val drawerLayout: DrawerLayout = binding.drawerLayout
        val navView: NavigationView = binding.navView
        val navController = findNavController(R.id.nav_host_fragment_content_main)

        appBarConfiguration = AppBarConfiguration(
            setOf(
                R.id.nav_home, R.id.nav_gallery, R.id.nav_slideshow
            ), drawerLayout
        )
        setupActionBarWithNavController(navController, appBarConfiguration)
        navView.setupWithNavController(navController)
    }

    override fun onCreateOptionsMenu(menu: Menu): Boolean {

        menuInflater.inflate(R.menu.main, menu)
        return true
    }

    override fun onSupportNavigateUp(): Boolean {
        val navController = findNavController(R.id.nav_host_fragment_content_main)
        return navController.navigateUp(appBarConfiguration) || super.onSupportNavigateUp()
    }
}

activity main.xml -

    <?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ui.slideshow.SlideshowFragment">

    <TextView
        android:id="@+id/text_slideshow"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:textAlignment="center"
        android:textSize="20sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <WebView
        android:id="@+id/webview"
        android:layout_width="409dp"
        android:layout_height="354dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

My manifest file -

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

    <application
        android:allowBackup="true"
        android:dataExtractionRules="@xml/data_extraction_rules"
        android:fullBackupContent="@xml/backup_rules"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.BestGlobeVPN"
        tools:targetApi="31">
        <activity
            android:name=".MainActivity"
            android:exported="true"
            android:label="@string/app_name"
            android:theme="@style/Theme.BestGlobeVPN.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

            <meta-data
                android:name="android.app.lib_name"
                android:value="" />
        </activity>
    </application>

</manifest>

log cat err. -

FATAL EXCEPTION: main Process: com.bestvpn.globevpn.myapplication, PID: 31177 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bestvpn.globevpn.myapplication/com.bestvpn.globevpn.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.loadUrl(java.lang.String)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3732) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3906) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:103) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2259) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loopOnce(Looper.java:210) at android.os.Looper.loop(Looper.java:299) at android.app.ActivityThread.main(ActivityThread.java:8105) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:556) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1045) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.loadUrl(java.lang.String)' on a null object reference at com.bestvpn.globevpn.myapplication.MainActivity.onCreate(MainActivity.kt:27) at android.app.Activity.performCreate(Activity.java:8251) at android.app.Activity.performCreate(Activity.java:8219) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1329) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3705) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3906)  at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:103)  at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)  at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2259)  at android.os.Handler.dispatchMessage(Handler.java:106)  at android.os.Looper.loopOnce(Looper.java:210)  at android.os.Looper.loop(Looper.java:299)  at android.app.ActivityThread.main(ActivityThread.java:8105)  at java.lang.reflect.Method.invoke(Native Method)  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:556)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1045)