Can't use priority queue in C# .NET 6

I'm trying to use PriorityQueue in C# with Unity and from the documentation it's said that .NET 6 is supported, and the needed namespace is System.Collections.Generic.

I've tried that:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using TMPro;

public class Test : Monobehaviour
{
    void Start()
    {
        var queue = new PriorityQueue<int, int>();
    }
}

But an error is thrown back:

The type or namespace name 'PriorityQueue<,>' could not be found (are you missing a using directive or an assembly reference?) [Assembly-CSharp]

I've checked the .NET version within VS Code:

So any idea why this is happening?