Fix issue 14049：The title of the collection editor for custom controls in .NET Core is incorrect.

src/System.Windows.Forms.Design/src/System/ComponentModel/Design/CollectionEditor.CollectionEditorCollectionForm.cs

@@ -56,7 +56,7 @@ public CollectionEditorCollectionForm(CollectionEditor editor) : base(editor)
                 ScaleButtonImageLogicalToDevice(_upButton);
             }
 
-            Text = string.Format(SR.CollectionEditorCaption, CollectionItemType.Name);
+            Text = string.Format(SR.CollectionEditorCaption, GetCollectionItemTypeNameForCaption(CollectionItemType));
 
             HookEvents();
 
@@ -76,6 +76,20 @@ public CollectionEditorCollectionForm(CollectionEditor editor) : base(editor)
             AdjustListBoxItemHeight();
         }
 
+        private static string GetCollectionItemTypeNameForCaption(Type collectionItemType)
+        {
+            string itemTypeName = collectionItemType.Name;
+
+            if (collectionItemType is { IsGenericType: true, GenericTypeArguments: [Type innerType] }
+                && typeof(Control).IsAssignableFrom(innerType)
+                && collectionItemType.GetGenericTypeDefinition().Name.StartsWith("ControlProxy", StringComparison.Ordinal))
+            {
+                itemTypeName = innerType.Name;
+            }
+
+            return itemTypeName;
+        }
+
         private bool IsImmutable
         {
             get

src/System.Windows.Forms.Design/tests/UnitTests/System/ComponentModel/Design/CollectionEditorTests.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
 #nullable disable
@@ -102,6 +102,16 @@ public void CollectionEditor_CreateCollectionForm_Invoke_Success()
         Assert.NotSame(form, editor.CreateCollectionForm());
     }
 
+    [Fact]
+    public void CollectionEditor_CreateCollectionForm_Caption_UnwrapsControlProxy()
+    {
+        SubCollectionEditor editor = new(typeof(List<ControlProxy<TestChildControl>>));
+        using Form form = editor.CreateCollectionForm();
+
+        Assert.Contains(nameof(TestChildControl), form.Text);
+        Assert.DoesNotContain("ControlProxy`1", form.Text);
+    }
+
     [Theory]
     [InlineData(typeof(object), typeof(object))]
     [InlineData(typeof(int[]), typeof(object))]
@@ -120,6 +130,14 @@ public void CollectionEditor_CreateCollectionItemType_Invoke_ReturnsExpected(Typ
         Assert.Same(itemType, editor.CreateCollectionItemType());
     }
 
+    private sealed class ControlProxy<TControl>
+    {
+    }
+
+    private sealed class TestChildControl : Control
+    {
+    }
+
     public static IEnumerable<object[]> InvalidDesignerHost_TestData()
     {
         yield return new object[] { null };