{....}

  private
    procedure WMNCHitTest(var Message: TWMNCHitTest); message WM_NCHITTEST;
    
{....}

procedure TForm1.WMNCHitTest(var Message: TWMNCHitTest);
begin
  inherited;

  with Message do
  begin
    if Result = HTCAPTION then
      Result := HTNOWHERE;
  end;
end;