How to enable $levels in oData .Net core 3.1

I have developed an oData server with .Net core 3.1.

Asp.net in its older versions support $levels for example check here.

In my server I can expand my queries until 2 levels. It means a URL like the following:

https://localhost:44375/odata.svc/Patients?$expand=PatientForms($expand=Form)

works in my server and I can see the expanded results. Now if I try to perform it with $levels:

https://localhost:44375/odata.svc/Patients?$expand=PatientForms($levels=2)

then I will get the following error:

The query specified in the URI is not valid. The $level option on navigation property 'PatientForms' is not allowed, because the related entity type 'mjzsoft.Models.PatientForm' could not be cast to source entity type 'mjzsoft.Models.Patient'.

The controllers for Patient and PatientForm and Form are as follows, however as they have exactly same structure with different model names, therefore, I just reflected one of them here:

[ODataRoutePrefix("Patients")]
    public class PatientsController : ODataController
    {
        private readonly XxxDbContext xxxDbContext;
        public PatientsController(XxxDbContext xxxDbContext)
                => this.xxxDbContext = xxxDbContext;
        
        [ODataRoute]
        [EnableQuery]
        //[PagingValidatorQuery]
        public IActionResult Get()
        {
            return Ok(this.xxxDbContext.Patients);
        }

        [ODataRoute("{id}")]
        [EnableQuery]
        public IActionResult Get([FromODataUri] ulong id)
        {
            return Ok(this.xxxDbContext.Patients.FirstOrDefault(item => item.Id == id));
        }

    }

In the database each Patient can have several Form. Hence, as this is an M to N relationship we have PatientForms in between.