Overload parameter does not work (maybe because of framework)

So i copied a sample of a website. Its about deserializing YAML into a object graph. I pasted the code into my projekt and most of it works. All the usings are the same. There is only one problem.

var deserializer = new Deserializer(namingConvention: new CamelCaseNamingConvention());

Here a new deserializer instance is created. but my vs underlines namingconvention red. The only difference of my project and the sample, is that my project uses .net core framework and the sample uses .net as a framework. I have honestly no actual clue what the difference between .net and .net core is apart from the fact that .net core is mostly used for server applications, and .net is used for normal applications. (I think lol)

Here is the sample I copied: https://dotnetfiddle.net/HD2JXM

Here is the error message:

var builder = new DeserializerBuilder();
var deserializer = builder
    .WithNamingConvention(CamelCaseNamingConvention.Instance)
    .Build();