<PackageReference Include="System.Net.Http.WinHttpHandler" Version="11.0.0-preview.1.26104.118" />

System.Net.Http.WindowsProxyUsePolicy

public enum WindowsProxyUsePolicy
This enumeration provides available options for the proxy settings used by an HttpClient when running on Windows.
namespace System.Net.Http { public enum WindowsProxyUsePolicy { DoNotUseProxy, UseWinHttpProxy, UseWinInetProxy, UseCustomProxy } }