Set Assembly version from dll under %APPDATA%

Question

I would like to get into my setup the version from the main dll of software to be installed.

This was not that hard to accomplish when the dll was in a fixed location where I used it to pass the BuildVersion to the wxs file as a DefinedConstant within a BeforeBuild:

<Target Name="BeforeBuild">
<GetAssemblyIdentity AssemblyFiles="$(TargetDir)\myApp.dll">
  <Output TaskParameter="Assemblies" ItemName="AssemblyVersion" />
</GetAssemblyIdentity>
<PropertyGroup>
  <DefineConstants>BuildVersion=%(AssemblyVersion.Version)</DefineConstants>
</PropertyGroup>

And for the AfterBuild I did do a not so important renaming, even I could do it in the CI/CD as well:

<Target Name="AfterBuild">
  <GetAssemblyIdentity AssemblyFiles="$(TargetDir)\myApp.dll">
    <Output TaskParameter="Assemblies" ItemName="AssemblyVersion" />
  </GetAssemblyIdentity>
  <Copy SourceFiles=".\bin\$(Configuration)\$(OutputName).exe" DestinationFiles=".\bin\$(Configuration)\myApp_%(AssemblyVersion.Version)_Setup.exe" />
  <Delete Files=".\bin\$(Configuration)\$(OutputName).exe" />
</Target>

But now that I want to use as ´AssemblyFiles´ the ´%APPDATA%´ I define the AssemblyFiles like this:

AssemblyFiles="%APPDATA%\myApp.dll"

And the expression is not found.

I have also tried:

<DefineConstants>PluginDir=%APPDATA%\myAppFolder;</DefineConstants>
AssemblyFiles="$(var.PluginDir)\myApp.dll"

But also did not work.

What's the exact syntax here? I have seen some people even creating MSBuild Tasks for this but I consider this overwhelming for such a simple thing that can be accomplished most of the time in such a simple way.