ParticleSpawner.cs

using System;
using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using UnityEngine.AddressableAssets;
using UnityEngine.ResourceManagement.AsyncOperations;

public class ParticleSpawner : MonoBehaviour
{
    [SerializeField] private List<AssetReference> _particleReferences;

    private Dictionary<AssetReference, List<GameObject>> _spawnedParticleSystems = new Dictionary<AssetReference, List<GameObject>>();
    private Dictionary<AssetReference, Queue<Vector3>> _queuedSpawnRequests = new Dictionary<AssetReference, Queue<Vector3>>();
    
    private Dictionary<AssetReference, AsyncOperationHandle<GameObject>> _asyncOperationHandles = 
        new Dictionary<AssetReference, AsyncOperationHandle<GameObject>>();

    public void Spawn(int index)
    {
        if (index < 0 || index >= _particleReferences.Count)
            return;

        AssetReference assetReference = _particleReferences[index];

        if (assetReference.RuntimeKeyIsValid() == false)
        {
            Debug.Log("Invalid Key " + assetReference.RuntimeKey.ToString());
            return;
        }

        if (_asyncOperationHandles.ContainsKey(assetReference))
        {
            if (_asyncOperationHandles[assetReference].IsDone)
                SpawnParticleFromLoadedReference(assetReference, GetRandomPosition());
            else
                EnqueueSpawnForAfterInitialization(assetReference);
            
            return;
        }

        LoadAndSpawn(assetReference);
    }

    private void LoadAndSpawn(AssetReference assetReference)
    {
        var op = Addressables.LoadAssetAsync<GameObject>(assetReference);
        _asyncOperationHandles[assetReference] = op;
        op.Completed += (operation) =>
        {
            SpawnParticleFromLoadedReference(assetReference, GetRandomPosition());
            while (_queuedSpawnRequests?[assetReference].Any() == true)
            {
                var position = _queuedSpawnRequests[assetReference].Dequeue();
                SpawnParticleFromLoadedReference(assetReference, position);
            }
        };
    }

    private void EnqueueSpawnForAfterInitialization(AssetReference assetReference)
    {
        if (_queuedSpawnRequests.ContainsKey(assetReference) == false)
            _queuedSpawnRequests[assetReference] = new Queue<Vector3>();
        _queuedSpawnRequests[assetReference].Enqueue(GetRandomPosition());
    }

    private void SpawnParticleFromLoadedReference(AssetReference assetReference, Vector3 position)
    {
        assetReference.InstantiateAsync(position, Quaternion.identity).Completed += (asyncOperationHandle) =>
        {
            if (_spawnedParticleSystems.ContainsKey(assetReference) == false)
            {
                _spawnedParticleSystems[assetReference] = new List<GameObject>();
            }
            
            _spawnedParticleSystems[assetReference].Add(asyncOperationHandle.Result);
            var notify = asyncOperationHandle.Result.AddComponent<NotifyOnDestroy>();
            notify.Destroyed += Remove;
            notify.AssetReference = assetReference;
        };
    }

    private Vector3 GetRandomPosition()
    {
        return new Vector3(UnityEngine.Random.Range(-5, 5), 0, UnityEngine.Random.Range(-5, 5));
    }

    private void Remove(AssetReference assetReference, NotifyOnDestroy obj)
    {
        Addressables.ReleaseInstance(obj.gameObject);
        
        _spawnedParticleSystems[assetReference].Remove(obj.gameObject);
        if (_spawnedParticleSystems[assetReference].Count == 0)
        {
            Debug.Log($"Removed all {assetReference.RuntimeKey.ToString()}");
            
            if (_asyncOperationHandles[assetReference].IsValid())
                Addressables.Release(_asyncOperationHandles[assetReference]);

            _asyncOperationHandles.Remove(assetReference);
        }
    }
}

public class NotifyOnDestroy : MonoBehaviour
{
    public event Action<AssetReference, NotifyOnDestroy> Destroyed;
    public AssetReference AssetReference { get; set; }

    public void OnDestroy()
    {
        Destroyed?.Invoke(AssetReference, this);
    }
}