Add test

src/Controls/tests/Xaml.UnitTests/Issues/Maui20616.xaml

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+<?xml version="1.0" encoding="UTF-8"?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             xmlns:local="clr-namespace:Microsoft.Maui.Controls.Xaml.UnitTests"
+             x:Class="Microsoft.Maui.Controls.Xaml.UnitTests.Maui20616">
+    <Label Text="{Binding Value}" x:DataType="local:ViewModel20616(x:String)" />
+    <Label Text="{Binding Value}" x:DataType="{x:Type local:ViewModel20616(x:String)}" />
+</ContentPage>

src/Controls/tests/Xaml.UnitTests/Issues/Maui20616.xaml.cs

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+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Globalization;
+using System.Linq;
+using Microsoft.Maui.ApplicationModel;
+using Microsoft.Maui.Controls.Core.UnitTests;
+using Microsoft.Maui.Controls.Shapes;
+using Microsoft.Maui.Devices;
+using Microsoft.Maui.Dispatching;
+
+using Microsoft.Maui.Graphics;
+using Microsoft.Maui.UnitTests;
+using NUnit.Framework;
+
+namespace Microsoft.Maui.Controls.Xaml.UnitTests;
+
+public partial class Maui20616
+{
+    public Maui20616()
+    {
+        InitializeComponent();
+        BindingContext = new ViewModel20616<string> { Value = "Foo" };
+    }
+
+    public Maui20616(bool useCompiledXaml)
+    {
+        //this stub will be replaced at compile time
+    }
+
+    [TestFixture]
+    class Test
+    {
+        [SetUp]
+        public void Setup()
+        {
+            Application.SetCurrentApplication(new MockApplication());
+            DispatcherProvider.SetCurrent(new DispatcherProviderStub());
+        }
+
+        [TearDown] public void TearDown() => AppInfo.SetCurrent(null);
+
+        [Test]
+        public void XDataTypeCanBeGeneric([Values(false, true)] bool useCompiledXaml)
+        {
+            if (useCompiledXaml)
+            {
+                MockCompiler.Compile(typeof(Maui20616));
+            }
+            else
+            {
+                new Maui20616(useCompiledXaml: false);
+            }
+        }
+    }
+}
+
+public class ViewModel20616<T>
+{
+    public required T Value { get; init; }
+}