free-programming-books VS Functional Programming in C#

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I'm not a fan of functional programming, but this book develops a library for it https://github.com/la-yumba/functional-csharp-code

Enterprise applications typically use OOP programming. I would like to ask if functional programming with C# is used in the real world? It seems to be a lot cleaner. I would like to use this library in a project but I am not sure if it would be advisable?