Decorator pattern prevent detection of unused method

Question

I have a decorator pattern with DI container registration:

public interface IFoo
{
    string Print();
}

public class Foo : IFoo
{
    public string Print() => "Foo";
}

public class Decorator(IFoo decorated) : IFoo
{
    public string Print()
    {
        return "=" + decorated.Print() + "=";
    }
}

IServiceCollection service;
services.AddTransient<IFoo, Foo>()
    .Decorate<Foo, Decorator>();

The issue is that in real application after I remove the last usage of the method/class, I cannot recognize that code is in reality unused.

I don't want to count the call in decorator as a reference usage so I can see that the method is unused (only decorated but unused).

Is there any attribute or other solution to achieve that in C#?