that isn't really coherent. it doea use c# as the main languahe for game logic and for some platforms the mono runtime

I've never used it, but know it uses C#; but after a quick perusal of the docs seems to use mono, not the Microsoft implementation even on windows:

https://docs.unity3d.com/Manual/WindowsDebugging.html

I assume conflicting terminology: Unity calls the core of the engine "runtime", and that is written in C++. If you write C# logic, then that calls through fairly thin bindings into that.

At the same time the C#/.net programs are executed by the Common Language Runtime.