I'm curious what you want to learn C# for? Do you need C# to script in Unity or are you wanting to modify Unity itself?
As far as I am aware, C# is used to build software like operating systems and applications, not so much for scripting within apps. That is usually Python. What are you looking to do?
Unity only supports c#. modifying unity could be helpful or cool but I'm not really looking to try something like that anytime soon. I looked into unreal engine, Godot, and android studio but I like unity and I want to continue using it. currently, I just am making little small test games until I can advance to an actual project maybe. and I'm also trying to learn HTML and c+ so I can make websites or at least A website.