Gist For https://blogs.bitesinbyte.com/posts/Cosmos_DB_Sdk_System_Text_Json_Issue/

CosmosSystemTextJsonSerializer.cs

public class CosmosSystemTextJsonSerializer : CosmosSerializer
{
    private readonly JsonObjectSerializer systemTextJsonSerializer;

    public CosmosSystemTextJsonSerializer(JsonSerializerOptions jsonSerializerOptions)
    {
        this.systemTextJsonSerializer = new JsonObjectSerializer(jsonSerializerOptions);
    }

    public override T FromStream<T>(Stream stream)
    {
        using (stream)
        {
          if (stream.CanSeek && stream.Length == 0)
          {
              return default;
          }

          if (typeof(Stream).IsAssignableFrom(typeof(T)))
          {
             return (T)(object)stream;
          }

          return (T)this.systemTextJsonSerializer.Deserialize(stream, typeof(T), default);
        }
    }

    public override Stream ToStream<T>(T input)
    {
        MemoryStream streamPayload = new MemoryStream();
        this.systemTextJsonSerializer.Serialize(streamPayload, input, input.GetType(), default);
        streamPayload.Position = 0;
        return streamPayload;
    }
}