PoolList.cs

using System;
using System.Collections.Generic;

public class PoolList<T>
{
	public List<(bool IsAvailable, T type)> Pool = new();

	public (bool success, (bool IsAvailable, T instance) item) TryGetFromPool(out T value)
	{
		for (int i = 0; i < Pool.Count; i++)
		{
			if (Pool[i].IsAvailable)
			{
				var item = Pool[i];

				item.IsAvailable = false;

				Pool[i] = item;

				value = item.type;

				return (success: true, item);
			}
		}

		value = default;

		return (success: false, (false, default));
	}

	public void ReturnToPool(T instance)
	{
		for (int i = 0; i < Pool.Count; i++)
		{
			var item = Pool[i];

			if (EqualityComparer<T>.Default.Equals(item.type, instance))
			{
				item.IsAvailable = true;
				Pool[i] = item;
				return;
			}
		}
	}

	/// <summary>
	/// Populates pool using custom initFunction that returns the object you want added to the pool.
	/// Example - Allows instantiating a prefab then returning it's CanvasGroup.
	/// </summary>
	public PoolList<T> Init(int size, Func<T> initFunction)
	{
		for (int i = 0; i < size; i++)
		{
			Pool.Add((IsAvailable: true, initFunction()));
		}

		return this;
	}
}