error: activity not declared in AndroidManifest.xml in Android Studio - android-studio

Question

My AndroidManifest.xml :
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
android:installLocation="auto">
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.RECORD_AUDIO" />
<uses-feature android:name="com.softbank.hardware.pepper" />
<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/Theme.TammyApp">
<activity android:name=".ui.categories.CategoriesActivity">
</activity>
# <activity android:name=".activities.Muse.muse_pick_duration" />
<activity android:name=".activities.Welcome">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<service android:enabled="true" android:name=".activities.SpeechService" />
</application>
</manifest>
/////////////////////////////////
muse_pick_duration.kt:
package com.tammy.tammyapp.activities.Muse
import com.tammy.tammyapp.R
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import com.tammy.tammyapp.activities.TutorialActivity
abstract class muse_pick_duration : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
setContentView(R.layout.muse_pick_duration)
super.onCreate(savedInstanceState)
}
}
/////////////////////////////////////////////////////////
museHome.kt:
package com.tammy.tammyapp.activities.Muse
import android.content.Intent
import android.os.Bundle
import android.widget.Button
import androidx.appcompat.app.AppCompatActivity
import com.tammy.tammyapp.R
import com.tammy.tammyapp.activities.TutorialActivity
abstract class MipniHome : AppCompatActivity(){
//abstract val muse_pick_duration: Unit
abstract val muse_pick_duration: Unit
abstract val savedInstanceState: Bundle?
fun onCreate() {
setContentView(R.layout.muse_home)
super.onCreate(savedInstanceState)
val button3 = findViewById<Button>(R.id.button3)
button3.setOnClickListener {
val Intent = Intent(this, muse_pick_duration::class.java)
startActivity(Intent)
}
}
}
///////////////////////////////////////////////////////
muse_home.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=".museHome">
// main menu button
<Button
android:id="#+id/button"
android:layout_width="100dp"
android:layout_height="60dp"
android:layout_marginStart="32dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="121dp"
android:layout_marginBottom="259dp"
android:backgroundTint="#3F51B5"
android:text="Main Menu"
android:textSize="16sp"
app:cornerRadius="10dp"
app:layout_constraintBottom_toTopOf="#+id/button2"
app:layout_constraintEnd_toStartOf="#+id/textView4"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0" />
// back button
<Button
android:id="#+id/button2"
android:layout_width="100dp"
android:layout_height="60dp"
android:layout_marginStart="16dp"
android:layout_marginBottom="16dp"
android:backgroundTint="#3F51B5"
android:text="Back"
android:textSize="16sp"
app:cornerRadius="10dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent" />
// next button
<Button
android:id="#+id/button3"
android:layout_width="100dp"
android:layout_height="60dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="16dp"
android:layout_marginBottom="16dp"
android:backgroundTint="#3F51B5"
android:text="Next"
android:textSize="16sp"
app:cornerRadius="10dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="1.0"
app:layout_constraintStart_toEndOf="#+id/textView3"
app:layout_constraintTop_toBottomOf="#+id/imageView"
app:layout_constraintVertical_bias="1.0" />
<TextView
android:id="#+id/textView2"
android:layout_width="216dp"
android:layout_height="56dp"
android:layout_marginStart="12dp"
android:layout_marginBottom="16dp"
android:text="Press "BACK" to return to the previous screen"
android:textSize="20sp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toEndOf="#+id/button2" />
<TextView
android:id="#+id/textView3"
android:layout_width="218dp"
android:layout_height="47dp"
android:layout_marginEnd="124dp"
android:layout_marginBottom="24dp"
android:text="Press "NEXT" when you are ready to continue"
android:textSize="20sp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
<TextView
android:id="#+id/textView4"
android:layout_width="508dp"
android:layout_height="63dp"
android:layout_marginTop="80dp"
android:layout_marginEnd="237dp"
android:layout_marginBottom="266dp"
android:text="Welcome to MIPNI,"
android:textAlignment="center"
android:textColor="#000000"
android:textSize="50sp"
app:layout_constraintBottom_toTopOf="#+id/textView2"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="#+id/button"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0" />
<TextView
android:id="#+id/textView5"
android:layout_width="370dp"
android:layout_height="28dp"
android:text="your musical companion app!"
android:textAlignment="center"
android:textColor="#000000"
android:textSize="20sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/textView4" />
<ImageView
android:id="#+id/imageView"
android:layout_width="502dp"
android:layout_height="256dp"
android:layout_marginBottom="23dp"
app:layout_constraintBottom_toTopOf="#+id/textView3"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.501"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/textView5"
app:layout_constraintVertical_bias="0.0"
app:srcCompat="#drawable/music" />
</androidx.constraintlayout.widget.ConstraintLayout>
//////////////////////////////////////////////
I attached my code above that includes a button(button3) trying to open another activity(muse_pick_duration) and the AndroidManifest.xml.
The bolded activity is the one that says is not declared but I did declare it... IDK what is going on. Can someone please help?!
I tried so invalidating the cache and restaring. I also tried syncing project with gradle files but mone of that worked. I have two activities: muse_pick_duration and museHome and both are in kotlin...