My perception is lots of libraries that does serious work are just written in C and C++, in the future I imagine they will be in Rust and not C# - I am talking libraries you get from NuGet, lots of well maintained ones have a C# API that is a shell around something from elsewhere. Be it ImageMagick, lots of media decoding stuff or even proprietary things, like Flir.
It's usually hard to find a library to do some work for you in C#, in NuGet, that is also maintained - you will have an easier time grabbing the sources and adding directly in your project so you can maintain it yourself as bug appears and debug it more easily. A lot of times the bug is the developer assumed everyone uses Windows.
Most of time when using C# I am reinventing the wheel in it because of this.
I also never had a C# project that used it exclusively.