Program.cs

using System;
using System.Globalization;
using System.Numerics;

char[] keys =
[
	'Q', 'W', 'E', 'R', 'T', 'Y', 'U', 'I', 'O', 'P',
	'A', 'S', 'D', 'F', 'G', 'H', 'J', 'K', 'L',
	'Z', 'X', 'C', 'V', 'B', 'N', 'M',
];

MainMenu:
Console.Clear();
Console.WriteLine(
	$"""
	 Clicker

	 In this game you will continually click
	 keys on your keyboard to increase your
	 score, but you cannot press the same key
	 twice in a row. :P You will start with
	 the [{keys[0]}] & [{keys[1]}] keys but unlock additional
	 keys as you click.

	 NOTE FROM DEVELOPER: Do not play this game.
	 Clicker games are nothing but a waste of
	 your time. I only made this game as an
	 educational example.

	 ESC: close game
	 ENTER: continue
	""");
MainMenuInput:
Console.CursorVisible = false;
switch (Console.ReadKey(true).Key)
{
	case ConsoleKey.Enter: break;
	case ConsoleKey.Escape:
		Console.Clear();
		Console.CursorVisible = true;
		return;
	default: goto MainMenuInput;
}

DateTime start = DateTime.Now;
BigInteger clicks = 0;
ConsoleKey previous = default;
Console.Clear();
while (true)
{
	string clicksString = clicks.ToString(CultureInfo.InvariantCulture);
	int keyCount = clicksString.Length + 1;

	if (keyCount > keys.Length)
	{
		TimeSpan duration = DateTime.Now - start;
		Console.Clear();
		Console.WriteLine(
		$"""
		 Clicker

		 You Win!

		 Your time: {duration}

		 ESC: return to main menu
		""");
		GameOverInput:
		Console.CursorVisible = false;
		switch (Console.ReadKey(true).Key)
		{
			case ConsoleKey.Escape: goto MainMenu;
			default: goto GameOverInput;
		}
	}

	Console.SetCursorPosition(0, 0);
	Console.WriteLine(
		$"""
		 Clicker

		 Clicks: {clicksString}

		 Keys: {string.Join(" ", keys[0..keyCount])}

		 ESC: return to main menu
		""");
	ClickerInput:
	Console.CursorVisible = false;
	ConsoleKey key = Console.ReadKey(true).Key;
	switch (key)
	{
		case >= ConsoleKey.A and <= ConsoleKey.Z:
			int index = Array.IndexOf(keys, (char)key);
			if (index < keyCount && key != previous)
			{
				previous = key;
				clicks += index > 1 ? BigInteger.Pow(10, index - 1) / (index - 1) : 1;
			}
			break;
		case ConsoleKey.Escape: goto MainMenu;
		default: goto ClickerInput;
	}
}