All classes that aren’t stock Java/Kotlin classes need an explicit import declaration at the top of the source file. (Either on the class directly or on the package

Hover over the View declaration that is highlighted in red. The pop-up dialog will offer you a link to “import class”. Click it.

This will add an import android.view.View; statement to the top of your source file.

Repeat the same thing for the Intent class as well.

I realised I was writing where I didn’t have to (inside the protected void onCreate). Here’s the corrected version:

public class activity_menuPrincipal extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EdgeToEdge.enable(this);
        setContentView(R.layout.activity_menu_principal);
        ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
            Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
            v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);
            return insets;
        });
            
    }
    *public void abrirCalculadora(View v){
        Intent openCalculadora = new Intent(this, MainActivity.class);
        startActivity(openCalculadora);*
    }
}