Installed and used as follows
<ItemGroup>
<PackageReference Include="MSBuild.EntityFrameworkCore.RemoveDesignerCompilation" Version="0.1.0-alpha6" />
</ItemGroup>
<PropertyGroup>
<RDC_Enabled>true</RDC_Enabled>
<RDC_DesignerFileCountToKeep>5</RDC_DesignerFileCountToKeep>
</PropertyGroup>
On build it removes all designer files, so the count property gets ignored somehow.
.net deps @ 7.0.13