Fix MarkdownTextBlock which is not working in multithreaded

components/MarkdownTextBlock/src/MarkdownConfig.cs

@@ -11,5 +11,7 @@ public record MarkdownConfig
     public ISVGRenderer? SVGRenderer { get; set; }
     public MarkdownThemes Themes { get; set; } = MarkdownThemes.Default;
 
-    public static MarkdownConfig Default = new();
+    [ThreadStatic]
+    private static MarkdownConfig? _default;
+    public static MarkdownConfig Default => _default ??= new MarkdownConfig();
 }

components/MarkdownTextBlock/src/MarkdownTextBlock.Properties.cs

@@ -15,7 +15,7 @@ public partial class MarkdownTextBlock
         nameof(Config),
         typeof(MarkdownConfig),
         typeof(MarkdownTextBlock),
-        new PropertyMetadata(new MarkdownConfig(), OnConfigChanged)
+        new PropertyMetadata(MarkdownConfig.Default, OnConfigChanged)
     );
 
     /// <summary>

components/MarkdownTextBlock/src/MarkdownThemes.cs

@@ -14,7 +14,9 @@ namespace CommunityToolkit.WinUI.Controls;
 
 public sealed class MarkdownThemes : DependencyObject
 {
-    internal static MarkdownThemes Default { get; } = new();
+    [ThreadStatic]
+    private static MarkdownThemes? _default;
+    internal static MarkdownThemes Default => _default ??= new MarkdownThemes();
 
     public Thickness Padding { get; set; } = new(8);