Flutter- Unresolved Class in Android Manifest for MainActivity and other Classes in the package for the kotlin code

<?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="in.packagename">
<activity
android:name=".MainActivity"
android:configChanges=
"orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|
locale|layoutDirection|fontScale|screenLayout|density|uiMode"
        android:exported="true"
        android:hardwareAccelerated="true"
        android:launchMode="singleTask"
        android:screenOrientation="portrait"
        android:theme="@style/LaunchTheme"
        android:windowSoftInputMode="adjustResize">

The IDE is showing unresolved class for MainActivity and other activities. I have done all things rebuild, restart, updating the IDE but nothing seems to work. Although the project is running fine with the functionalities of kotlin code but showing error in IDE.