I can't give you any benchmarks, but in my experience (from wrapping a big C++ game engine in generated C#), modern .NET interop overhead is basically unnoticea

I can't give you any benchmarks, but in my experience (from wrapping a big C++ game engine in generated C#), modern .NET interop overhead is basically unnoticeable. .NET 7 finally also ships with NativeAOT which compiles your C# to native code that you can expose as a C library.