telling apart Rect class in different assemblies of c# eco system

I am working on a WinUI3 project, in the dependencies my frameworks are stated as Microsoft.NETCore.App and Microsoft.Windows.SDK.Net.Ref. I need a class to represent a rectangular geometry. I have found an already defined class: https://learn.microsoft.com/en-us/dotnet/api/system.windows.rect?view=windowsdesktop-9.0

It seems this class is within WindowsBase assembly that I have within my project under `Microsoft.NETCore.App framework, but I don't know how to reference it https://referencesource.microsoft.com/#WindowsBase,namespaces

Online it is listed under Windows Desktop 9 (which means Windows Presentation Foundation?), anyway I cannot reference this class from within my project.

Can however reference Windows.Foundation.Rect https://learn.microsoft.com/en-us/uwp/api/windows.foundation.rect?view=winrt-26100 but it misses much of the functionality I need such as IntersectsWith(Rect), Offset, etc...

Also can reference System.Drawing.Rectangle https://learn.microsoft.com/en-us/dotnet/api/system.drawing.rectangle?view=net-8.0 which is listed under .NET but in the description says is designed for Windows Forms which I heard is to be discontinued

So first, I don't understand why I can access one but not the other, also what should I do? To be honest I spent so much time trying to make sense of it all that perhaps it would be better to implement everything with my own code.

Solution

as Simon Mourier Commented the solution was to add <UseWPF>true</UseWPF> to .csproj project file

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net8.0-windows10.0.19041.0</TargetFramework>
    <TargetPlatformMinVersion>10.0.17763.0</TargetPlatformMinVersion>
    <UseWPF>true</UseWPF>

However it breaks the project as WinUI auto generated code didn't work propertly.