I programmed a button to change screens in Android studio but it keeps crashing when I try and open it

Question

I have been trying to learn android studio and I wanted to make a button that transitioned from one screen to the other Here is my code for it:

public class MainActivity extends AppCompatActivity {

        private AppCompatActivity AppCompatActivity;
        private TextView openingText;
        private Button alarmButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        openingText = findViewById(R.id.openingText);

        nextButton();
    }

    //this function causing issues (maybe because more than just button on screen)
    private void nextButton(){
        Button calculatorButton = (Button) findViewById(R.id.backButton);
        calculatorButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view){
                startActivity(new Intent(MainActivity.this, Calculators.class));
            }
        });
    }
}

(I only made the calculator screen for now, only that button should work) Followed this tutorial: https://www.youtube.com/watch?v=6RtF_mbHcEc&ab_channel=AdobeinaMinute But every time I try to run the app, it just crashes. Without the button function, it works tho. Is there something I'm missing?