repro.cs

public class TestEnumerator2
{
    public string Name { get; set; }

    public bool IsSucceed { get; set; }

    public ObservableCollection<int> Toto { get; set; }

    public TestEnumerator2()
    {
        Toto = new ObservableCollection<int>();
    }
}

var serialize = JsonSerializer.Serialize(new TestEnumerator2(),new JsonSerializerOptions { ReferenceHandler = System.Text.Json.Serialization.ReferenceHandler.Preserve});
var deserialize = JsonSerializer.Deserialize<TestEnumerator>(serialize);