✅ ERROR: The calling thread cannot access this object because a different thread owns it.

private void AddChatMessage(string username, string message, System.Drawing.Color usernameColor)
{
    System.Windows.Media.Color mediaColor = System.Windows.Media.Color.FromArgb(usernameColor.A, usernameColor.R, usernameColor.G, usernameColor.B);

    var usernameRun = new Run(username)
    {
        Foreground = new SolidColorBrush(mediaColor),
        FontWeight = FontWeights.Bold
    };
    var messageRun = new Run(": " + message)
    {
        Foreground = Brushes.White
    };

    var paragraph = new Paragraph();
    paragraph.Inlines.Add(usernameRun);
    paragraph.Inlines.Add(messageRun);

    // Ensure the UI update is done on the UI thread
    chatRichTextBox.Dispatcher.Invoke(() =>
    {
        chatRichTextBox.Document.Blocks.Add(paragraph);
        chatRichTextBox.ScrollToEnd();
    });
}