Many older .NET applications saved programmers from this by providing "C# scripts". The framework includes the compiler and then it's trivial to use the compiled artifact. You can still do it by including the Roslyn libraries. I don't see it as much anymore, or it's some half-baked Python or Lua interface.

The new Roslyn incremental generator API is pretty good these days but not well documented yet. I’ve been using it with json-schema to save a lot of boilerplate and provide a more intuitive declarative framework in a large side project.