There's a good pluralsight course by Zoran Horvat called, "Writing purely functional code in C#" ( https://www.pluralsight.com/courses/writing-purely-functiona... ), where he explores exactly that.
Modern C# has added a bunch of things which means you don't need to write it in the OOP style, although if you find yourself working for others then OOP is what they'll likely expect.
There's a good pluralsight course by Zoran Horvat called, "Writing purely functional code in C#" ( https://www.pluralsight.com/courses/writing-purely-functiona... ), where he explores exactly that.
Modern C# has added a bunch of things which means you don't need to write it in the OOP style, although if you find yourself working for others then OOP is what they'll likely expect.