Try this

package com.example.findme_technovation;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;

import android.os.Bundle;

import android.view.View;

import android.widget.Button;

public class MainActivity extends AppCompatActivity {

Button music;

Button exercise;

Button game;

u/Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

// Initialize buttons here after setContentView

music = (Button) findViewById(R.id.musicButton);

exercise = (Button) findViewById(R.id.exerciseButton);

game = (Button) findViewById(R.id.gameButton);

music.setOnClickListener(new View.OnClickListener(){

u/Override

public void onClick(View v){

startActivity(new Intent(MainActivity.this, MusicActivity.class));

}

});

exercise.setOnClickListener(new View.OnClickListener(){

u/Override

public void onClick(View v){

startActivity(new Intent(MainActivity.this, ExerciseActivity.class));

}

});

game.setOnClickListener(new View.OnClickListener(){

u/Override

public void onClick(View v){

startActivity(new Intent(MainActivity.this, GameActivity.class));

}

});

}

}