How can I add a reference to PresentationCore to an existing .NET 5 class library?

How can I add a reference to PresentationCore to an existing .NET 5 class library?

Set TargetFramework and UseWPF:
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFramework>net5.0-windows</TargetFramework>
<UseWPF>true</UseWPF>
</PropertyGroup>
</Project>