I did some Android studio tutorials and made an App with Kotlin. On 1 screen all works as I like but open a 2nd screen via a button wont work

To access a 2nd screen via a button on the 1st screen I followed internet tutorials, so I inserted

• a 2nd activity and
• a 2nd layout.

In the 2nd layout I added e.g. a textView and
in the 1st activity I added a button:

package com.example.inko_gnito

import android.content.Intent
import android.os.Bundle
import android.widget.Button
import android.widget.Toast
import androidx.activity.ComponentActivity

class MainActivity : ComponentActivity() {
private lateinit var startbutton: Button
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.main_screen)
    startbutton = findViewById(R.id.startbutton)
    startbutton.setOnClickListener {
        val intent = Intent(this, Playerselect::class.java)
        startActivity(intent)
    }
}
}`

When I run the 1st activitx it works as always. When I click the button to access the 2nd screen the layout of the 2nd screen does not appear but only the smart phone device main screen.
What am I doing wrong? Do I have something to do in the manifest for example?

I followed for example this tutorial:
https://www.youtube.com/watch?v=2gljhNFKimk
and it seems to work very simple. AFter checking out some tips on the manifest I don't get any further after 1 day.

Thanks in advance for Your help, it must be something simple I'm missing.

thanks for the quick response, I now found my mistake myself. The manifest needed 2 further lines which were automatically created in the tutorials but not the way I created the 2nd MainActivity2. Manifest must look like this:

    <activity
        android:name=".PlayerSelect"
        android:exported="false"
        android:label="@string/title_activity_player_select"
        android:theme="@style/Theme.Inko_Gnito" />

--> I was missing the two last lines. That happens when one (as me) not enters a new "empty activity" but any another one (I could not fine the "empty activity" as it was shown in the tutorials, but now did).