C# equivalent of Schema library?

I currently use Colyseus for a TypeScript/browser project and really like it. I especially like its Schema library, because after getting the basic things running (server, client, rooms, state) it is sooooo easy to add (and change and remove) variables which are automatically synchronized from the server to the client.

Can anybody recommend a pure C# library which provides exactly that feature (making adding and changing synchronized variables as easy as possible)?

On its GitHub page Schema lists some libraries under "inspiration" (protocol buffers, flatbuffers, schemapack, avro) but those don't seem to completely provide what I am looking for (only serialization, not the whole incremental delta synchronization).

I am aware that Colyseus has a C#/Unity client but in a project with a C#/Unity client I would prefer a C# server because having the same programming language everywhere makes things easier in my opinion.

We don't have any C# server as you want, but why not use Colyseus as server for your Unity client? That's why schema make sense.