.NET 10 adds ReferenceHandler support directly inside JsonSourceGenerationOptionsAttribute

Program.cs

using System.Text.Json.Serialization;

// Giving you fine-grained control over how cycles and references are handled at the source generation leve
[JsonSourceGenerationOptions(ReferenceHandler = JsonKnownReferenceHandler.Preserve)]
[JsonSerializable(typeof(Employee))]
internal partial class AppJsonContext : JsonSerializerContext { }