Enable button from another Form [Answered]

        private void OpenChildForm(Form childForm, object btnSender)
        {
            if (btnSender is null)
            {
                throw new ArgumentNullException(nameof(btnSender));
            }

            _activeForm?.Close();

            _activeForm = childForm;
            childForm.TopLevel = false;
            childForm.FormBorderStyle = FormBorderStyle.None;
            childForm.Dock = DockStyle.Fill;
            this.panelDesktop.Controls.Add(childForm);
            this.panelDesktop.Tag = childForm;
            childForm.BringToFront();
            childForm.Show();
        }