Prevent a collection from being serialized by default in .NET 6 webapi application

Question

I have 2 classes: Item and ItemClass and Item is referenced as a Collection in ItemClass:

public class ItemClass : DbEntityInteger, IDbInternalcodeEntity, IDbNameEntity
{
    public ItemClass()
    {
        Items = new List<Item>();
    }
    public virtual string InternalCode { get; set; }
    //[System.Text.Json.Serialization.JsonIgnore]
    public virtual IList<Item> Items { get; set; }
    public virtual string? Name { get; set; }
}

I've developed a webapi including OData Query Language so i'd like to have this behavior: Items Property must be serialized only when i use the $expand command otherwise a request to the api that return Item Classes must have this property empty.

I tried to decore Items Property with System.Text.Json.Serialization.JsonIgnore attributre but obviously the property is no longer serialized, but, if i remove the attribute the Items Collection is alwayse serialized, even without the using of $expand.

2022-04-12 edit:
According to this example and this video I only added this code in my project:
Startup:
builder.Services.AddControllers().AddOData(options => options.Select().Filter().OrderBy().Expand().Count().SetMaxTop(50).SkipToken());
Controller:
Add [EnableQuery] on method Get of my ItemClassController.

But this is not enough.
According to this other example, Controller must inherits from ODataController or implements [ODataAttributeRouting] and in Startup the EdmModel must be defined and declared in AddControllers().
Startup:

static IEdmModel GetEdmModel()
{
    ODataConventionModelBuilder builder = new();
    builder.EntitySet<ItemClass>("ItemClasses");
    return builder.GetEdmModel();
}
[...]
builder.Services.AddControllers().AddOData(opt => opt.AddRouteComponents("odata", GetEdmModel())
                                        .Select()
                                        .Filter()
                                        .OrderBy()
                                        .Expand()
                                        .Count()
                                        .SetMaxTop(50)
                                        .SkipToken()
);

ItemClassController:

public class ItemClassesController : ODataController
    {
        private readonly ILogger<ItemsController> _logger;
        private readonly IItemManager _itemManager;

        public ItemClassesController(ILogger<ItemsController> logger, IItemManager itemManager)
        {
            _logger = logger;
            _itemManager = itemManager;
        }

        [EnableQuery(PageSize = 15)]
        public ActionResult<IEnumerable<Test.Core.ItemClass>> Get()
        {
            IEnumerable<Test.Core.ItemClass> result;
            result = _itemManager.ItemClassSessionMapper.Elements;
            return new ActionResult<IEnumerable<Test.Core.ItemClass>>(result);
        }
    }

Now it works, subclasses are not expanded by default and response is encapsulated in odata context:

  "@odata.context": "http://localhost:5253/odata/$metadata#ItemClasses",
  "value": [
    {
      "InternalCode": "TST",
      "Name": "Test Class",
      "Id": 3,
      "Version": 0,
      "UniqueKey": "4b01b1a6-8042-44d2-9eb2-a1c9ef7f86cf",
      "DateTimeCreated": "2022-04-12T08:48:33.8578697+02:00",
      "DateTimeModified": null,
      "UserCreated": null,
      "UserModified": null,
      "Note": null,
      "DateTimeLoadedInSession": "2022-04-12T17:23:43.8772784+02:00"
    }
  ]
}

Unfortunately expand works with single reference property but not with collections, I suppose could depend on this version of OData which is still under development.
This is part of the exception message I get when I try to expand Items Collection:

 ---> System.ArgumentException: Argument types do not match
   at System.Linq.Expressions.Expression.Condition(Expression test, Expression ifTrue, Expression ifFalse)
   at NHibernate.Linq.ReWriters.SubQueryConditionalExpander.SubQueryFromClauseExpander.VisitConditional(ConditionalExpression node)

2022-04-14 edit:
Solved!
The issue with $Expand "Argument types do not match" was due to this reason:
in ItemClassesController I returned ItemClass Elements as IEnumerable<Test.Core.ItemClass> but, in ItemClass object the property Items was public virtual IList<Item> Items { get; set; } and it seems that OData service is unable to cast form IList to IEnumerable.
Changing Get method resolves the issue:

        [HttpGet]
        [EnableQuery(PageSize = 100)]
        public ActionResult<IList<Test.Core.ItemClass>> Get()
        {
            IList<Test.Core.ItemClass> result;
            result = _itemManager.ItemClassSessionMapper.Elements.ToList();
            return new ActionResult<IList<Test.Core.ItemClass>>(result);
        }

This is not Nhibernate Layer fault because if I deactivate OData and return an IEnumerable<Test.Core.ItemClass>, Items collection is correctly serialized.