How can I browse this site curriculum? Is this only for front end?
You’re browsing the forum, if you look at the URL and remove /forum/ just leaving www.freecodecamp.org it will put you at the main site. Once you’re at the main site you will see curriculum at the top right, or at the bottom if you scroll down. There you can get started learning to code and see all the lessons this site offers.
To answer the question in the title: no, FCC does not have a C# curriculum. The only programming language taught by the curriculum is JavaScript.
We do have sub-forums for PHP and Python, so we might consider adding C# in the future. However the pool of C# expertise here isn’t terribly large, so you’d probably be better off on a site that specializes in C#/.NET for now.
I agree with @chuckadams . Talk to developers at www.stackoverflow.com . I’m sure they can help you to find good C# resources. ALSO, the Microsoft team just launched this learning platform with several videos for .NET technologies: https://dotnet.microsoft.com/learn/videos?WT.mc_id=-blog-scottha