Over simplified Blockchain

Picochain.cs

if(System.Environment.GetCommandLineArgs().Length == 0) {
    Console.Write("Add something to the blockchain:\n> ");
    AddBlock(Console.ReadLine());
} else {
    switch (System.Environment.GetCommandLineArgs()[0]) {
        case "-v": CheckBlockChain(); break;
        default: AddBlock(System.Environment.GetCommandLineArgs()[0]); break;
    }
}

static void AddBlock(string msg) {
    var blockchain = LoadBlockChain();
    if(!CheckBlockChain(blockchain)) return;
    blockchain.Add(Block.New(blockchain.Count, msg, HashBlock(blockchain.Last(), msg)));
    Console.WriteLine($"New Block #{blockchain.Last().Id} added to the blockchain - {blockchain.Last().Hash}");
    SaveBlockChain(blockchain);
}

static bool CheckBlockChain(List<Block> blockchain = null) {
    blockchain = blockchain ?? LoadBlockChain();
    for(int i = 1; i<blockchain.Count; i++) 
        if(HashBlock(blockchain[i-1], blockchain[i]) != blockchain[i].Hash) {
            Console.Error.WriteLine($"Blockchain is not valid - Block: #{i} - {blockchain[i].Hash} does not belong there.");
            return false;
        }
    return true;
}

static string HashBlock(Block prevBlock, Block block) => 
    Convert.ToBase64String(System.Security.Cryptography.SHA256.Create()
    .ComputeHash(Encoding.UTF8.GetBytes($"{prevBlock.Id}{prevBlock.Value}{prevBlock.Hash}{block.Id}{block.Value}")));

static List<Block> LoadBlockChain() => 
    System.IO.File.Exists("blockchain.json") 
    ? System.Text.Json.JsonSerializer.Deserialize<List<Block>>(System.IO.File.ReadAllText("blockchain.json")) 
    : new List<Block> { Block.New(0, "Genesis Block") };

static void SaveBlockChain(List<Block> blockchain) => 
    System.IO.File.WriteAllText("blockchain.json", System.Text.Json.JsonSerializer.Serialize(blockchain, 
    new System.Text.Json.JsonSerializerOptions { WriteIndented = true }));

public struct Block { 
    public int Id { get; set; } 
    public string Value { get; set; } 
    public string Hash { get; set; } 
    public static Block New(int id, string value, string hash = "") => new Block { Id = id, Value = value, Hash = hash };
}