Are "partially" unbound generics possible?

Question

I came across Generics open and closed constructed types this question and started toying around with typeof. I am now wondering why I can do this:

var t = typeof(IPipelineBehaviour<,>);

but not this

var s = typeof(IPipelineBehaviour<,List<>>);

Here is a minimal example for use with https://dotnetfiddle.net/

using System;
using System.Collections.Generic;                   

public class Program
{
    public static void Main()
    {
        var t = typeof(IPipelineBehaviour<,>);
        Console.WriteLine(t);
        
        var s = typeof(IPipelineBehaviour<,List<>>);
        Console.WriteLine(s);
    }
}

public interface IPipelineBehaviour<TRequest,TResult>
{

}

---

I am trying to register an unbound generic for an MediatR.IPipelineBehaviour for which I can assert, that TResult is of type OneOf (see https://github.com/mcintyre321/OneOf ).

I tried to assert it in the class definition through a where clause such as this

public class MyBehaviour<TRequest,TResult> : IPipelineBehaviour<TRequest,TResult>
    where TRequest : IRequest<TResult>
    where TResult : OneOf<???,Problem>
{
    // Implementation goes here
}

but in that case I am lacking the Type indicated as ??? and now I am trying to approach it as follows:

services.AddTransient(typeof(IPipelineBehaviour<,Oneof<,>>), typeof(ValidationBehaviour<,OneOf<,>>);

but it does not work, because typeof(IPipelineBehaviour<,Oneof<,>>) cannot be evaluated.