ゲームの攻略本って英語でなんて言うの？

Walkthrough can also be used in the sense of rehearsal (in theatre) or testing (in software production)

Explanation: Some people may look upon the use of these tips, hints snd shortcuts as a 'cheat' as the challenge element of the game is removed.
Example sentence:
"I couldn't find my way out of the haunted castle so I got some wallkthrough tips online."

A walk-through is a tour of an area or demonstration of how to complete a task.

A cheat sheet is a text that guides people how to complete something without having to work out the answers by themselves.

The book or instructions that tell you how to play the game can be called the "Manual" or a "strategy book"

The term strategy guide is most commonly used but the term walkthrough is also used to explain the manuals people can use to find hints and cheats to finish a video game. Strategy guides are written for specific games. For example: I need to see the strategy guide for Fortnite.

A "cheat sheet" can be a book or list of hints, codes, and shortcuts that can be used for a video game.

To describe the book that helps you get through a video game quickly, you could call it a 'walkthrough manual'. This phrase is more formal and correct, it is probably what the game company would actually call it. However, in casual conversation, many natives call this a 'cheat sheet' which describes the fact that you are getting through the game with extra help, something some people would term as cheating.

When you want to explain that there is a book explaining how to play a particular game and how to finish it; then you can use the following phrases:
-A game manual
-A book explaining how to play and finish a game.
-A how-to game guide