What is the best way to handle JSON in Unity?

JsonUtility cannnot handle Nullable(Nullable クラス (System) | Microsoft Learn), so I have stopped using it.

I have found Newtonsoft Json


but is it the best way to handle JSON in Unity?

Persoanally i would highly recommend using Odin Serializer (not to be confused with Odin inspector).
Odin serializer in part of Odin inspector and it’s open source and free to use and download.
Odin also has a Unity integration layer where you can use it to serialize MonoBehaviour and ScriptableObjects , but for what you need it should look something like this