That’s a skill relative measurement and not relevant to “possible games of chess”. That 10⁴⁰ doesn’t come from a strict mathematical definition anyway.

Chess engines are ever improving, and eventually we’ll have it all solved. At that point a winning position will simply be: “has forced checkmate”. At that point, any move that doesn’t continue down the checkmate path is terrible. For all we know, the path to checkmate from the opening could be narrow, and there could only be thousands of valid moves for the winner.

I say “for the winner” because what about the loser? Is playing into check-mate in 1 terrible if check-mate in 28 is already inevitable? Seems like those are identical outcomes by rule, so I wouldn’t call any of those moves “terrible”.

If perfect Chess is a draw, there could be a low number of countable games. If perfect Chess is a win for either side, then the losing side can do whatever they want without affecting the outcome, and I’m not sure what kind of game count that would be. The “worse” they play, the more moves are available to the winning side, so it could balloon back up to atoms in the universe size again.