Why do you need to hard code a reference to a parent form from a child form?

Here is a simple example:

I have two forms.  Form 1 and Form 2.  Form 2 is opened by pressing a button on form 1.  Form 1 also contains a method that might be called by form 2.  So you usually pass a reference as follows

public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Form2 form2 = new Form2(this);
            form2.Show();
        }

        public void showMessage()
        {
            MessageBox.Show("from form1");
        }
    }

Now in Form2 I have

 public partial class Form2 : Form
    {
        Form1 _parent = null;
             
        
        public Form2(Form1 frm)
        {
            InitializeComponent();
            _parent = frm;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            _parent.showMessage();
        }

Now this works fine.  However, what if you need to open Form2 from a different form??  The name of Form1 is hard coded in Form2.  What if I have a form34 that needs to show form2 also?  Do I need another copy of form2?

In other words, I need to have code in Form2 that does not explicitly state the calling parent form but rather give me the name of it and then I can have logic to determine what the calling form was and then call an appropriate method in the calling form. How could I do this?

Thanks