Found actually the solution:
While all project has configuration similar to next, the platform is AnyCpu
<PropertyGroup>
<TargetFramework>net6.0</TargetFramework>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
<Platforms>AnyCPU</Platforms>
</PropertyGroup>
Test project should have
<TargetFramework>net6.0-windows10.0.22621.0</TargetFramework>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
<Platforms>ARM32;AnyCPU</Platforms>
<ResolveAssemblyWarnOrErrorOnTargetArchitectureMismatch>
None
</ResolveAssemblyWarnOrErrorOnTargetArchitectureMismatch>
<GenerateAssemblyInfo>false</GenerateAssemblyInfo>
<EnableDefaultEmbeddedResourceItems>false</EnableDefaultEmbeddedResourceItems>
<UseWindowsForms>true</UseWindowsForms>
<UseWPF>true</UseWPF>
<ImportWindowsDesktopTargets>true</ImportWindowsDesktopTargets>
<IsTestProject>true</IsTestProject>
<EnableNETAnalyzers>false</EnableNETAnalyzers>
<OutputPath>bin\$(Configuration)</OutputPath>
The most important here is ARM32 ( do not know why but it works)