Wrong. The sheer number of different possible moves in just the first few moves is incredible. There is no such thing as the perfect set of moves. After the first move there are hundreds of possibilities. After that hundreds of thousands, after that millions. Nobody can possibly remember every possibility for any given game opening.
What are different types of chess games?
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What you are talking about is the transition between theoretical "book" opening moves and other moves.
To put it simply, there are so many openings and variations White can play, and so many ways Black can answer, and so many ways both sides can play, defensively or aggressively, during the middlegame, that we will never be able to study them all.
Nonetheless, it is true most positions have already been obtained up until the middlegame.
And lastly, yes, it is most often a inaccuracy made by one of the two players that makes the transition between "book" moves and other moves. However, it can also be an "interesting" move, which, for example, is a bit risky.
@1
"shouldn't every game they play be the same?"
++ No. Chess is a draw. White has many objectively equivalent choices.
For each of those black has some adequate defenses. Here is proof:
https://www.iccf.com/event?id=100104
All perfect games without mistakes, all draws, different openings, different games.
"any deviation from the "ideal game" would indicate a mistake by one of the players"
++ No. Any decisive game indicates a mistake by one of the players.
Iam beginner in chess, I have a question that might sound naive, but I'd appreciate it if you could hear me out. https://ehallpass.pro
Considering that grandmasters and international masters extensively study the best moves in chess and must have reached conclusions, shouldn't every game they play be the same? If there is an objectively best move in each situation, why don't they consistently play the exact same game? It seems that any deviation from the "ideal game" would indicate a mistake by one of the players, right?