For example, you might need to create an instance of one class from an instance of another class, ... A custom object mapper example in C#. Let us now dig into a bit of code.

I won't say that, all by itself, C# 9 is worth the migration to .NET 5 (I might make that claim about C# 8 and .NET Core 3.x, though). The new version of C# 9 is more than just a nice feature of .NET ...