选用了 AngleSharp + AngleSharp.Xml

<ItemGroup>
  <PackageReference Include="AngleSharp" Version="1.3.0" />
  <PackageReference Include="AngleSharp.Xml" Version="1.0.0" />
</ItemGroup>

Program.cs

using AngleSharp;

var config = Configuration.Default.WithXml();
using var httpClient = new HttpClient();

var svg = await httpClient.GetStringAsync("https://www.cnblogs.com/images/logo.svg");
var document = await BrowsingContext.New(config).OpenAsync(res => res.Content(svg));
var svgElement = document.QuerySelector("svg");

Console.WriteLine("element: " + svgElement);
Console.WriteLine("width: " + svgElement?.GetAttribute("width"));
Console.WriteLine("height: " + svgElement?.GetAttribute("height"));

// output:
// element: AngleSharp.Svg.Dom.SvgSvgElement
// width: 150
// height: 55

参考：How can I parse an SVG?