The main differences between Func<string,string> and a custom delegate are:
Syntax
Func<string,string> is a built-in generic delegate in C# that represents a method with a string parameter and a string return type. It's defined as public delegate TResult Func<in T, out TResult>(T arg);
A custom delegate is defined using the delegate keyword, e.g. public delegate string StringTransformer(string input);
Flexibility
Func<string,string> is limited to methods with a string parameter and string return type.
A custom delegate can represent any method signature, e.g. taking multiple parameters of different types, returning void, etc.
