When you do want a class

Classes are fully supported. Reach for one when you want to create nodes with new without a store (seed data, tests, an import job), want behaviour on the type, or deserialise straight into it from an external feed. A class can also implement an interface: the interface is the queryable contract, and the class a form you can create. A class has four extra obligations:

public class Organizer : IOrganizer {
    public Guid Id { get; set; }

    // The attributes are on IOrganizer: repeating them here has no effect.
    public string Name { get; set; } = string.Empty;
    public string ContactEmail { get; set; } = string.Empty;
    public string Slug { get; set; } = string.Empty;
    public DateTime CreatedUtc { get; set; }

    public NodeMeta Meta { get; set; } = NodeMeta.Empty;   // get and set on a class
}

A parameterless constructor is required. The model builder throws without one.
Initialise every reference-typed member: string.Empty, FileValue.Empty, NodeMeta.Empty, [] for embedded maps, new() for relation and reference properties. Interfaces need none of this.
Meta has a setter. Still never build one: start with NodeMeta.Empty.
Attributes go on the interface when the class implements one.

Records and structs work too. A record needs the record Foo() { … } form to have a parameterless constructor. Structs are supported but rarely worth it.