OData function no longer working as expected

I have just updated a project to NET 6 and OData 8.0.6.. I have a function that is no longer working as expected.

Method Definition:

public virtual async Task<IActionResult> GetComparitiveTable(
    [FromODataUri] string cultureCode,
    ODataQueryOptions<ComparitiveLocalizableString> options)
{
    if (!CheckPermission(ReadPermission))
    {
        return Unauthorized();
    }
    else
    {
        int tenantId = GetTenantId();
        var connection = GetDisposableConnection();

        var query = connection.Query(x => x.TenantId == tenantId && (x.CultureCode == null || x.CultureCode == cultureCode))
		    .ToHashSet()
            .GroupBy(x => x.TextKey)
            .Select(grp => new ComparitiveLocalizableString
            {
                Key = grp.Key,
                InvariantValue = grp.First(x => x.CultureCode == null).TextValue,
                LocalizedValue = grp.FirstOrDefault(x => x.CultureCode == cultureCode) == null
                    ? string.Empty
                    : grp.First(x => x.CultureCode == cultureCode).TextValue
            })
            .AsQueryable();

        var results = options.ApplyTo(query, IgnoreQueryOptions);
        var response = await Task.FromResult((results as IQueryable<ComparitiveLocalizableString>).ToHashSet());
        return Ok(response);
    }
}

Note that an entity is queried (LocalizableString) and a complex type is returned (ComparitiveLocalizableString).

Definition of LocalizableString:

public class LocalizableString : TenantEntity<Guid>
{
	public string CultureCode { get; set; }

	public string TextKey { get; set; }

	public string TextValue { get; set; }
}

Definition of ComparitiveLocalizableString:

public class ComparitiveLocalizableString
{
    public string Key { get; set; }

    public string InvariantValue { get; set; }

    public string LocalizedValue { get; set; }
}

OData Function Setup:

var getComparitiveTableFunction = builder.EntityType<LocalizableString>().Collection.Function("GetComparitiveTable");
getComparitiveTableFunction.Parameter<string>("cultureCode");
getComparitiveTableFunction.Returns<IActionResult>();

URL:

${this.apiUrl}/Default.GetComparitiveTable(cultureCode='${this.cultureCode}')

Error:

Microsoft.OData.ODataException: The key value (Default.GetComparitiveTable(cultureCode='en-US')) from request is not valid. The key value should be format of type 'Edm.Guid'.

I'm not trying to query by the entity's key, but by it's CultureCode, as I have specified in the OData function definition (and which has been working fine for several versions of AspNetCoreOData until now).