Found 2 packages
SgmlReader is a .NET library that is handy for converting SGML content (like HTML and OFX) into well formed XML via XmlReader, XmlDocument, XDocument or XPathDocument. It runs on Windows and Linux using .NET core.
Netstandard Version of Dave Ragget's Tidy Library based on Tidy.NET (http://sourceforge.net/projects/tidynet/) updated to include html 5 tags.