Beyond considerations of FIDE rating, personal pride and in some cases national pride, the objective of the game is to checkmate the opponent's king, and that's what Firouzja and Prag were bravely trying to do in their critical games when they were already out of contention. This is absolutely not tournament manipulation.
However, there is a real issue that one player's free selection of risk level can indeed have an impact on other players' chances of winning the tournament. One comment in the coverage chat, that commentator Danny Rensch picked up on and supported, is that Nepo was maybe happy that Fabi won in the penultimate round, in that it meant Fabi was now committed to playing for a win against Nepo in the final round.
It is also widely considered that in the Soviet era, game results were often fixed (arranged draws & sometimes concessions) to help ensure that desired GMs won events.
Most people would say, I think, that unsporting behaviour consists of not trying hard enough to win: being willing to accept a draw or even a loss.
But even here, there are limits to how much a player can be expected to try to win. Suppose a player has developed a secret opening innovation they are holding in reserve. They can surely be forgiven for not exposing that innovation in a game that does not matter. Or if the choice is between 40%/0%/60% estimated win/draw/loss chance and 10%/80%/10%, then maybe they should pick the latter option, which maximizes the expectation of rating improvement.
This is a difficult area, but it's in the nature of the game. One thing is clear, if a player genuinely tries to win, that can only be commended. I can't find anything in the FIDE Laws which covers this area, but in my opinion, such behaviour actively improves the overall repute of chess.
If any arbiters with their superior experience, would like to comment on this grey area, I would be grateful. A game with similar tournament structures, Magic the Gathering, had a similar challenge. Their resolution was (1) players do have the option to agree a draw before the game is started (2) in the final round, pairings are chosen to match tie-breakers as much as possible, so the motivation for agreeing a draw is as similar as possible. I've been out of tournament play for some years, so it might have changed but this mechanism worked quite well, and I mention it for reference.
I commend the positive spirit with which Firouzja & Prag approached their critical games in the penultimate round, when they were both already out of contention. This was a tremendous tournament, that reflected well on all the players, organizers & commentators.
And what a triumph by Gukesh Dommaraju, only 17 years old. I am humbled.
