Made it work, but still some debug code remains.

AvaloniaCoreRTDemo.csproj

@@ -1,9 +1,23 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <OutputType>WinExe</OutputType>
+    <OutputType>Exe</OutputType>
     <TargetFramework>net5.0</TargetFramework>
+	<!-- This is a hack. Avalonia 0.9.7 depends on a version of System.Reactive prior 4.4.1, which contains a critical fix for building with CoreRT -->
     <RestorePackagesWithLockFile>true</RestorePackagesWithLockFile>
+    <Platforms>AnyCPU;x64</Platforms>
   </PropertyGroup>
+  
+  <PropertyGroup>
+	<RootAllApplicationAssemblies>false</RootAllApplicationAssemblies>
+	<IlcGenerateCompleteTypeMetadata>true</IlcGenerateCompleteTypeMetadata>
+	<IlcGenerateStackTraceData>true</IlcGenerateStackTraceData>
+	<IlcDisableUnhandledExceptionExperience>false</IlcDisableUnhandledExceptionExperience>
+  </PropertyGroup>
+  
+  <ItemGroup>
+    <NativeLibrary Include="WindowsApp.lib" />
+  </ItemGroup>
+  
   <ItemGroup>
     <Compile Update="**\*.xaml.cs">
       <DependentUpon>%(Filename)</DependentUpon>
@@ -17,8 +31,13 @@
     <PackageReference Include="Avalonia.Desktop" Version="0.9.7" />
     <PackageReference Include="Avalonia.ReactiveUI" Version="0.9.7" />
     <PackageReference Include="Microsoft.DotNet.ILCompiler" Version="1.0.0-alpha-*" />
+	<!-- This is a hack. Avalonia 0.9.7 depends on a version of System.Reactive prior 4.4.1, which contains a critical fix for building with CoreRT -->
     <PackageReference Include="System.Reactive" Version="4.4.1" />
   </ItemGroup>
+  <ItemGroup>
+	<!-- Avalonis relies heavily on reflection. Describe types needed here. -->
+    <RdXmlFile Include="rd.xml" />
+  </ItemGroup>
   <ItemGroup>
     <None Update="avalonia.png" CopyToPublishDirectory="PreserveNewest">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>

AvaloniaCoreRTDemo.sln

@@ -8,13 +8,19 @@ EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
+		Debug|x64 = Debug|x64
 		Release|Any CPU = Release|Any CPU
+		Release|x64 = Release|x64
 	EndGlobalSection
 	GlobalSection(ProjectConfigurationPlatforms) = postSolution
 		{41A52A04-F7D8-4981-9546-DB020E54851D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{41A52A04-F7D8-4981-9546-DB020E54851D}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{41A52A04-F7D8-4981-9546-DB020E54851D}.Debug|x64.ActiveCfg = Debug|x64
+		{41A52A04-F7D8-4981-9546-DB020E54851D}.Debug|x64.Build.0 = Debug|x64
 		{41A52A04-F7D8-4981-9546-DB020E54851D}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{41A52A04-F7D8-4981-9546-DB020E54851D}.Release|Any CPU.Build.0 = Release|Any CPU
+		{41A52A04-F7D8-4981-9546-DB020E54851D}.Release|x64.ActiveCfg = Release|x64
+		{41A52A04-F7D8-4981-9546-DB020E54851D}.Release|x64.Build.0 = Release|x64
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

rd.xml

@@ -0,0 +1,44 @@
+<Directives>
+  <Application>
+	<!-- main app assembly provides types which needs to be reflected upon -->
+	<Assembly Name="AvaloniaCoreRTDemo" Dynamic="Required All"></Assembly>
+  
+	<!-- these are needed when you show images and draw text -->
+	<Assembly Name="Avalonia.Animation" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Themes.Default" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Visuals" Dynamic="Required All"></Assembly>
+	<Assembly Name="SkiaSharp" Dynamic="Required All"></Assembly>
+	
+	<!-- Not known if and when you need these:
+	<Assembly Name="Avalonia.Controls" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Base" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Interactivity" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Layout" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Markup" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Markup.Xaml" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Styling" Dynamic="Required All"></Assembly>
+	
+	<Assembly Name="Avalonia.DesktopRuntime" Dynamic="Required All"></Assembly>
+	
+	<Assembly Name="Avalonia.DesignerSupport" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Diagnostics" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Dialogs" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Input" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Logging.Serilog" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.OpenGL" Dynamic="Required All"></Assembly>
+	
+	<Assembly Name="Avalonia.Desktop" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Direct2D1" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.ReactiveUI" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Skia" Dynamic="Required All"></Assembly>
+	<Assembly Name="Avalonia.Win32" Dynamic="Required All"></Assembly>
+	
+	<Assembly Name="SkiaSharp" Dynamic="Required All"></Assembly>
+	<Assembly Name="ReactiveUI" Dynamic="Required All"></Assembly>
+	<Assembly Name="System.Reactive" Dynamic="Required All"></Assembly>
+	<Assembly Name="Splat" Dynamic="Required All"></Assembly>
+	-->
+	
+  </Application>
+</Directives>

test.cmd

@@ -1,2 +1 @@
-rem dotnet publish -o Publish  -r win-x64 -c release 
+dotnet publish -r win-x64 -c release /p:RestoreLockedMode=true
-dotnet publish -o Publish  -r win-x64 -c release /p:RestoreLockedMode=true