I have recently updated the MarkdownSharpCore library to support .NET 6.0. Previously the 1.1 version only supported .NET Standard 2.1 and .NET Core 2.2. The source code for the library can be found on GitHub at https://github.com/jasongaylord/markdownsharp. You can grab the NuGet package here: https://www.nuget.org/packages/MarkdownSharpCore.
MarkdownSharpCore allows you to present Markdown in the browser as HTML. There are a few applications that go the other route including Html2Markdown.