OnBackpressed Fragment transaction doesn't work but app closes

Question

I implemented a code for closing app from secondary Activity ...but in secondary Activity there are Fragments also and the problem is when I jumped into any Fragment and I pressed back button app directly closes .. my aim is to first Fragment-transaction's addToBackStack should work then app should close

This is the code in UserActivity's onBackPressed() method where I implemented Fragments:

public void onBackPressed() {
    DrawerLayout drawerLayout = findViewById(R.id.drawerLayout);
    if (drawerLayout.isDrawerOpen(GravityCompat.START)) {
        drawerLayout.closeDrawer(GravityCompat.START);
    } else {
        Intent intent = new Intent(UserActivity.this, MainActivity.class);
        intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        intent.putExtra("EXIT", true);
        startActivity(intent);
    }
}

Below code is in MainActivity's onCreate() method to finish Activity:

if (getIntent().getBooleanExtra("EXIT",false)) {
    finish();
}

and here are Fragments put in UserActivity:

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
    Fragment fragment;
    switch (item.getItemId()) {
        case R.id.setting:
            fragment = new SettingFragment();
            break;
        case R.id.logOut:
            SharedPreference.setLoggedIn(this,null,false);

            Intent intent = new Intent(UserActivity.this,MainActivity.class);
            startActivity(intent);

        default:
            fragment = null;
    }
    FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
    fragmentTransaction.replace(R.id.userFragment,fragment).addToBackStack(null).commit();
    drawerLayout.closeDrawer(GravityCompat.START);
    return true;
}