public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
 
        private void button1_Click(object sender, EventArgs e)
        {
            Form2 form2 = new Form2();
            form2.Show();
 
            button1.Enabled = false;
            label1.Text = "Button deaktiviert";
        }
    }

public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
        }
 
        private void Form2_FormClosing(object sender, FormClosingEventArgs e)
        {
            Form1 form1 = new Form1();
 
            form1.label1.Text = "Button aktiviert";
            form1.button1.Enabled = true;
        }
    }

Form1 form1 = new Form1();

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