Example of polymorphic serialisation with JsonUtility

Collectable.cs

using UnityEngine;
using System;

[Serializable]
public class Collectable : PolymorphicObject
{
    public string Name;
}

Data.cs

using UnityEngine;

public class Data : ScriptableObject
{
    public virtual void Save(string key)
    {
        var data = JsonUtility.ToJson(this);
        PlayerPrefs.SetString(key, data);
        PlayerPrefs.Save();
    }

    public virtual void Load(string key)
    {
        var data = PlayerPrefs.GetString(key);
        JsonUtility.FromJsonOverwrite(data, this);
    }
}

Engine.cs

using System;

[Serializable]
public class Engine : Module
{    
    public float Acceleration;
    public float MaxSpeed;    
}

FuelTank.cs

using System;

[Serializable]
public class FuelTank : Module
{
    public float Capacity;
}

Module.cs

public class Module : Collectable
{ 
}

Player.cs

using System.Collections.Generic;
using UnityEngine;
using System;
using System.Linq;

[CreateAssetMenuAttribute(menuName="Data/Player")]
public class Player : Data
{
    private const string SaveKey = "Player";

    [NonSerialized]
    public List<Collectable> cargo;
    
    [SerializeField]
    private List<string> cargoSerialised;
    
    public void Save()
    {
        cargoSerialised = cargo.Select(c => JsonUtility.ToJson(c)).ToList();
        base.Save(SaveKey);
    }

    public void Load()
    {
        base.Load(SaveKey);
        cargo = cargoSerialised.Select(c => Collectable.FromJson<Collectable>(c)).ToList();
        sectorUpdate.OnLoad();
    }

    [ContextMenu("Clear data")]
    private void ClearData()
    {
        PlayerPrefs.DeleteKey(SaveKey);
        cargo.Clear();
    }
}

PolymorphicObject.cs

using UnityEngine;
using System;

/// <summary>
/// Inherit from this class to allow polymorphic (de)serialisation via JsonUtility. 
/// Inheriting classes should be marked as [System.Serializable]
/// </summary>
public abstract class PolymorphicObject
{
    [HideInInspector]
    public string AssemblyQualifiedName; // for deserialising as the correct type
    public string TypeName; // for displaying the friendly type name in the inspector

    public static T FromJson<T>(string json) where T : PolymorphicObject
    {
        // deserialise first as PolymorphicObject to get the instance Type
        var type = Type.GetType(JsonUtility.FromJson<T>(json).AssemblyQualifiedName);
        
        // deserialise as the correct type
        return (T)JsonUtility.FromJson(json, type);
    }

    public PolymorphicObject()
    {
        // AssemblyQualifiedName is public and will be serialised
        // when using JsonUtility.ToJson
        var type = this.GetType();
        AssemblyQualifiedName = type.AssemblyQualifiedName;
        TypeName = type.Name.Split(',')[0];
    }
}

Shield.cs

using System;

[Serializable]
public class Shield : Module
{
    public float Hitpoints;
    public float RegenAmount;
    public float RegenSpeed;
}

Weapon.cs

using System;

[Serializable]
public class Weapon : Module
{
    public float RateOfFire;
    public float Damage;
}