Android drawable menu options are not clickable

Question

I want to create a drawable menu for my android app, currently using Java. I followed this tutorial: https://www.geeksforgeeks.org/navigation-drawer-in-android/

Mainactivity.java

...
  public DrawerLayout drawerLayout;
  public ActionBarDrawerToggle actionBarDrawerToggle;
...

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

        // drawer layout instance to toggle the menu icon to open
        // drawer and back button to close drawer
        drawerLayout = findViewById(R.id.my_drawer_layout);
        actionBarDrawerToggle = new ActionBarDrawerToggle(this, drawerLayout, R.string.nav_open, R.string.nav_close);

        // pass the Open and Close toggle for the drawer layout listener
        // to toggle the button
        drawerLayout.addDrawerListener(actionBarDrawerToggle);
        actionBarDrawerToggle.syncState();

        // to make the Navigation drawer icon always appear on the action bar
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    }

@Override
    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
        Toast.makeText(getApplicationContext(), "funciona", Toast.LENGTH_SHORT).show();

        if (actionBarDrawerToggle.onOptionsItemSelected(item))
        {
            return true;
        }
        switch (item.getItemId()) {
            case R.id.firstitem:
                Toast.makeText(getApplicationContext(), "obre", Toast.LENGTH_SHORT).show();
                return true;

        }
        return super.onOptionsItemSelected(item);

activity_main.xml There is a big relativeLayout and some linearLayouts, at the very end, this code:

   <com.google.android.material.navigation.NavigationView
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        app:menu="@menu/navigation"
        android:fitsSystemWindows="true"
        />

</androidx.drawerlayout.widget.DrawerLayout>

navigation.xml

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    tools:ignore="HardcodedText">

    <item
        android:id="@+id/firstitem"
        android:title="first item" />

    <item
        android:id="@+id/seconditem"
        android:title="Second item" />
    </menu>

The code does compile, opens the menu and shows the first Toast ("funciona"), options are highlighted when you press them but nothing shows up. I wanted to open a new activity but I can't get the new Toast ("obre") to show up. It's seems like there is something missing with the switch case and I can't figure it out. I tried using the if-else, to no avail.

Thank you