winforms tooltips / hover / hint on a button

unfortunately the only way is to use another control (no property on the button itself)
you can implement your own onmouse_over effect, but the easiest way is as follow:

 private void MyWin_Load(object sender, EventArgs e)
    var ToolTipX = new System.Windows.Forms.ToolTip();
    ToolTipX.SetToolTip(this.button123, "you are hovering over the button");