There are N implementations of actors on C# - e.g. in Orleans or Akka.Net. I see no problems with implementing these on C# - honesty, I don't even understand what kind of issues or lacks you anticipate. My only guess is that you assume channel-like abstraction is missing in C#, but that's not true: see System.Threading.Channels.

What's more is that C# actually adds aot of flexibility to the scene here:
- Custom schedulers
- Custom async machine builders
- And even custom tasks (see e.g. UniTask).