Adding bicep publish-extension into your csproj

Directory.Build.targets

<Project>
    <PropertyGroup>
        <!-- All the identifiers to target -->
        <RuntimeIdentifiers>win-x64;linux-x64;osx-arm64</RuntimeIdentifiers>

        <BicepCmdBase>bicep publish-extension</BicepCmdBase>
		<BicepCmdOsx>--bin-osx-arm64 "$(MSBuildProjectDirectory)/bin/$(Configuration)/$(TargetFramework)/osx-arm64/publish/$(AssemblyName)"</BicepCmdOsx>
		<BicepCmdLinux>--bin-linux-x64 "$(MSBuildProjectDirectory)/bin/$(Configuration)/$(TargetFramework)/linux-x64/publish/$(AssemblyName)"</BicepCmdLinux>
		<BicepCmdWin>--bin-win-x64 "$(MSBuildProjectDirectory)/bin/$(Configuration)/$(TargetFramework)/win-x64/publish/$(AssemblyName).exe"</BicepCmdWin>
		<BicepCmdTarget>--target "$(MSBuildProjectDirectory)/bin/$(AssemblyName)"</BicepCmdTarget>
		<BicepCmdForce>--force</BicepCmdForce>

		<!-- Concatenate all parts into a single command -->
		<BicepCommand>$(BicepCmdBase) $(BicepCmdOsx) $(BicepCmdLinux) $(BicepCmdWin) $(BicepCmdTarget) $(BicepCmdForce)</BicepCommand>
    </PropertyGroup>

    <!-- Make an ItemGroup so I can loop on the Identity property -->
	<ItemGroup>
		<RIDs Include="$(RuntimeIdentifiers)" />
	</ItemGroup>
	
    <!-- Loops on each RID but sets property BuildingMultiRid=true to avoid an infinite loop -->
    <Target Name="PublishForAllRids" BeforeTargets="Publish" Condition="'$(BuildingMultiRid)' != 'true'">
        <MSBuild Projects="$(MSBuildProjectFile)" Targets="Publish" Properties="RuntimeIdentifier=%(RIDs.Identity);BuildingMultiRid=true" BuildInParallel="true" />
        <Message Text="✅ Finishing multi-RID publish for: $(RuntimeIdentifiers)" Importance="high" />
    </Target>

    <!-- Call the bundle command but avoid calling it in the 3 runs so $(BuildingMultiRid) != true -->
	<Target Name="PackageBicepExtension" 
			DependsOnTargets="PublishForAllRids" 
			AfterTargets="Publish"
			Condition="'$(BuildingMultiRid)' != 'true'">
		<Message Text="📦 Packaging Bicep extension..." Importance="high" />
		<Exec Command="$(BicepCommand)" />
	</Target>
</Project>

MyExtension.csproj

<Project Sdk="Microsoft.NET.Sdk">

	<PropertyGroup>
		<OutputType>Exe</OutputType>
		<RootNamespace>MyExtension</RootNamespace>
		<AssemblyName>bicep-ext-myextension</AssemblyName>
		<IncludeNativeLibrariesForSelfExtract>true</IncludeNativeLibrariesForSelfExtract>
		<PublishSingleFile>true</PublishSingleFile>
		<SelfContained>true</SelfContained>
		<InvariantGlobalization>true</InvariantGlobalization>
		<TargetFramework>net9.0</TargetFramework>
		<Nullable>enable</Nullable>
		<ImplicitUsings>enable</ImplicitUsings>
	</PropertyGroup>

	<ItemGroup>
		<PackageReference Include="Azure.Bicep.Local.Extension" Version="0.38.33" />
	</ItemGroup>
</Project>