I have many instances of a class that instantiates prefabs that only exist in the editor. When this happens, an event is invoked to alert subscribers that things are being instantiated:

using UnityEngine;
using System;

public class GameObjectCreator : MonoBehaviour 
{
    [SerializeField]
    private GameObject _prefab;

    public event Action<GameObject> OnCreated;

    public void Create()
    {
        var clone = Instantiate(_prefab);
        OnCreated?.Invoke(clone);
    }
}

I am pairing this class with a few helper classes that have different responsibilities for setting up these clones; these helper classes also exist only within the editor. I am using OnValidate to subscribe to the OnCreated event, which allows everything to work inside Unity, but things break in an actual build.

public class CreationHelper : MonoBehaviour
{
    [SerializeField]
    private GameObjectCreator _creator;

    private void DoSomeStuff(GameObject gameObject) 
    {
        // ...
    }

    private void OnValidate() 
    {
        _creator.OnCreated += DoSomeStuff; // This is lost at runtime
    }
}

I know I can simply use a manager for additional setup within a given scene, but am wondering if there is a way to serialize event subscriptions so I can continue with this current structure.

I do not believe UnityEvents will work because they require concrete references to things in the scene, and I am instantiating an unknown number of prefabs at runtime.