Legend Item Text is not visible in Windows11Dark. This is because the LegendItem  A possible workaround is to subscribe to the VisualItemCreating event. In the event handler, we can create a new LegendItemElement and set its ForeColor.

private void LegendElement_VisualItemCreating(object sender, LegendItemElementCreatingEventArgs e)
{            
    e.ItemElement = new LegendItemElement(e.LegendItem) { ForeColor = Color.Black };
}