program.cs

// See https://aka.ms/new-console-template for more information
using System.Net.Http.Json;

Console.WriteLine("Hello, World!");

HttpClient http = new();
var customers = await http.GetFromJsonAsync<List<Customer>>("https://excel2json.io/api/share/dcb51ae600934ecf93c02c9ffcda3c6f");

foreach (var item in customers)
{
    Console.WriteLine(item.PostalCode);
}

Console.ReadLine();

public record Customer
{
    public string CustomerID { get; set; }
    public string CompanyName { get; set; }
    public string ContactName { get; set; }
    public string ContactTitle { get; set; }
    public string Address { get; set; }
    public string City { get; set; }
    public string Region { get; set; }
    public object PostalCode { get; set; }
    public string Country { get; set; }
    public string Phone { get; set; }
    public string Fax { get; set; }
}