Android

    //creation instance du la base
    databaseReference = FirebaseDatabase.getInstance().getReference().child("user").child("authenification_User");


    isncritUser.setOnClickListener(new View.OnClickListener() {
        <a href="https://www.codeproject.com/Members/OverRide">@Override</a>
        public void onClick(View v) {

            if(txtLogin.getText().toString().isEmpty()
                    && editPassworduser.getText().toString().isEmpty()
                    && num.getText().toString().isEmpty()
                    && email.getText().toString().isEmpty()
                    && verifPassworduser.getText().toString().isEmpty() )
            {
                Toast.makeText(InscriptionUser.this,"Remplir les chomps",Toast.LENGTH_SHORT).show();
            }
            else if(txtLogin.getText().toString().isEmpty()
                    || editPassworduser.getText().toString().isEmpty()

                    ||  verifPassworduser.getText().toString().isEmpty()
                    ||  num.getText().toString().isEmpty()
                    ||  email.getText().toString().isEmpty()

            )
            {
                Toast.makeText(InscriptionUser.this,"Remplir Tout les chomps",Toast.LENGTH_SHORT).show();
            }




            else if(!verifPassworduser.getText().toString().equals(editPassworduser.getText().toString()))
            {
                Toast.makeText(InscriptionUser.this,"Password ne pas vrai",Toast.LENGTH_SHORT).show();
            }
            else if(!txtLogin.getText().toString().isEmpty()
                    && !editPassworduser.getText().toString().isEmpty()
                    && !verifPassworduser.getText().toString().isEmpty()
                    && !verifPassworduser.getText().toString().isEmpty()
                    && !num.getText().toString().isEmpty()
                    && !email.getText().toString().isEmpty()
                    &&verifPassworduser.getText().toString().equals(editPassworduser.getText().toString())
            )
            {
                insert();
                Intent i=new Intent(InscriptionUser.this,profilUser.class);
                startActivity(i);
            }
            else{
                Toast.makeText(InscriptionUser.this,"Verifier  votre connexion",Toast.LENGTH_SHORT).show();
            }

        }
    });

}



private void  insert()
{
    String login=txtLogin.getText().toString();
    String password=editPassworduser.getText().toString();
    String numero=num.getText().toString();
    String mail=email.getText().toString();

      user user=new user(login,password,numero,mail);
      //pour gener un unique key a chaque user en utlise push
      databaseReference.push().setValue(user);
      Toast.makeText(InscriptionUser.this,"user inserted",Toast.LENGTH_SHORT).show();

I know that there are similar question like this, but none of the solutions work for me.
I want to create a folder in my root directory like whatsapp but i did not get it to work.
I was able to create a folder in my package folder but same method did not work for root directory

    //works for creating folder in my package directory
    File pk = new File(this.getExternalFilesDir("/myweb").getAbsolutePath());
    
    pk.mkdir();
    
    
    //this did not work for creating folder in root directory like whatsapp
    File root = new File(Environment.getExternalStorageDirectory() + "/myweb");
    
    root.mkdir();

How can i solve this problem