public class Test
    {        
        public int CorrectAnswers { get; set; }
        public bool GiveTime { get; set; }
        public int ID { get; set; }
        public double ItemsPerSecond { get; set; }
        public bool JustNewPLUs { get; set; }
        public string ListID { get; set; }
        public int MaxPLU { get; set; }
        public int MinPLU { get; set; }
        public string PLUListID { get; set; }
        public bool Passed { get; set; }
        public double Percent { get; set; }
        public int Points { get; set; }
        public int Querys { get; set; }
        public int TimeInSeconds { get; set; }
        public DateTime TimeOfTesting { get; set; }
        public bool Tiomekeeping { get; set; }
        public bool doTimekeeping { get; set; }
    }

public class RootObject
    {
       public List<Helper> PoolData { get; set; }
    }

public class Helper
    {
        public string ID { get; set; }
        public Test _Test { get; set; }
    }     

string json = System.IO.File.ReadAllText(@"C:/Projects/file.json");
var tmp = JsonConvert.DeserializeObject<RootObject>(json);

var tmp = JsonConvert.DeserializeObject<Dictionary<string, Test>>(json);

using System;
using System.Collections.Generic;
using System.Text.Json;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            string json = System.IO.File.ReadAllText(@"test.json");
            var tmp = JsonSerializer.Deserialize<Dictionary<string, FirebaseEntry>>(json);

            Console.Read();
        }
    }


    public class FirebaseEntry
    {
        // Deine Properties hier
    }
}