I write C# professionally. I think every programmer should learn one functional language that doesn’t have same escape hatches like example F# does meaning they are immutable only. It will make you better programmer in the end even if you choose C#. I also think Elixir is easy to learn functional language. It’s also dynamic language and C# is static typed. If I where you I would learn both if you can starting from Elixir so you might gravitate towards better design in C#.
C# can be also be quite complex language with multiple ways to do same things. Also you have to think about things like thread safety and that means using locks etc. But C# might have better lot better job opportunities depending on where you live.
