activity/exha/1 matches the site

public static Activity Manet_and_Modern_Beauty()
{
    var activity = new Activity()
        .WithContext()
        .WithId("https://linked.art/example/activity/exha/1")
        .WithLabel("Manet and Modern Beauty (Getty)")
        .WithClassifiedAs(Aat.Term("300054766", "Exhibiting"));

    activity.IdentifiedBy = [ new Name("Manet and Modern Beauty").AsPrimaryName() ];

    activity.ReferredToBy = [
        new LinguisticObject()
            .WithClassifiedAs(Aat.Description, Aat.Statement)
            .WithContent("The great painter of modern Paris Edouard Manet famously shocked contemporary audiences with his provocative pictures. The first exhibition ever to explore the last years of his short life, Manet and Modern Beauty highlights a less familiar and more intimate side of this celebrated artist's work.")
    ];

    activity.TimeSpan = new LinkedArtTimeSpan()
    {
        BeginOfTheBegin = new LinkedArtDate(2019, 10, 8),
        EndOfTheEnd = new LinkedArtDate(2020, 1, 12).EndOfDay()
    };

    activity.TookPlaceAt = [
        Tgn.Place("7023900", "Los Angeles")
            .WithClassifiedAs(Aat.City)
    ];

    activity.CarriedOutBy = [
        Ulan.Group("500115988", "Getty Museum")
            .WithClassifiedAs(Aat.Museum)
    ];

    activity.UsedSpecificObject = [
        new Set()
            .WithId("https://linked.art/example/set/exhset")
            .WithLabel("Exhibition objects") 
    ];
    activity.InfluencedBy = [
        new PropositionalObject()
            .WithId("https://linked.art/example/concept/exhidea")
            .WithLabel("Idea for Manet and Modern Beauty")
    ];

    return activity;
}

• Metatype classification The second argument classifies the first, not the object: WithClassifiedAs(Aat.Description, Aat.Statement) says this is a Description, and Description is a kind of Statement. The Plain C# form shows the nesting.
• Role shortcuts AsPrimaryName, AsAccessionNumber and AsSystemAssignedNumber each add a single classification, with the AAT terms Primary Name, Accession Number and System Number.
• Terms outside the registry The vocabulary registry holds only the terms linked.art itself publishes, so a dataset's own concepts, places and people are written with Aat.Term, Tgn.Place and Ulan.Person, giving the id and the label.

var activity = new Activity
{
    Context = ["https://linked.art/ns/v1/linked-art.json"],
    Id = "https://linked.art/example/activity/exha/1",
    Label = "Manet and Modern Beauty (Getty)",
    ClassifiedAs = [Aat.Term("300054766", "Exhibiting")],
    CarriedOutBy =
    [
        new Group
        {
            Id = "http://vocab.getty.edu/ulan/500115988",
            Label = "Getty Museum",
            ClassifiedAs = [Aat.Museum],
        },
    ],
    IdentifiedBy =
    [
        new Name("Manet and Modern Beauty")
        {
            ClassifiedAs = [Aat.PrimaryName],
        },
    ],
    TimeSpan = new LinkedArtTimeSpan
    {
        BeginOfTheBegin = new LinkedArtDate(2019, 10, 8),
        EndOfTheEnd = new LinkedArtDate(2020, 1, 12, 23, 59, 59),
    },
    TookPlaceAt =
    [
        new Place
        {
            Id = "http://vocab.getty.edu/tgn/7023900",
            Label = "Los Angeles",
            ClassifiedAs = [Aat.City],
        },
    ],
    UsedSpecificObject =
    [
        new Set
        {
            Id = "https://linked.art/example/set/exhset",
            Label = "Exhibition objects",
        },
    ],
    ReferredToBy =
    [
        new LinguisticObject
        {
            Content = "The great painter of modern Paris Edouard Manet famously shocked contemporary audiences with his provocative pictures. The first exhibition ever to explore the last years of his short life, Manet and Modern Beauty highlights a less familiar and more intimate side of this celebrated artist's work.",
            ClassifiedAs =
            [
                new Type("http://vocab.getty.edu/aat/300435416", "Description")
                {
                    ClassifiedAs = [Aat.Statement],
                },
            ],
        },
    ],
    InfluencedBy =
    [
        new PropositionalObject
        {
            Id = "https://linked.art/example/concept/exhidea",
            Label = "Idea for Manet and Modern Beauty",
        },
    ],
};

Generated from the object the example builds: every property that is set, as object initialisers, with the vocabulary constants where a term is in the registry. The fluent helpers are a convenience, not a requirement; this form and the one as written produce the same JSON.