What I meant by "solved" is "never loses from the starting position against Stockfish that has infinite time per move".
replyIn the TCEC game, I see "2. f4?!", so I'm guessing Stockfish was forced to played some specific opening, i.e. it was forced to make a mistake.
That means that Stockfish's parameters are already optimized as far as practically possible for Rapid chess and Slow chess, not that chess itself is solved, or even that Stockfish is fully optimized for Blitz and Bullet.
replySurely it is apparent to you that the first few moves are not independently chosen by the engine, but rather intentionally chosen by the TCEC bookmakers to create a position on the edge between a draw and a decisive result.
replyFor what it's worth, Stockfish wins the rematch also. https://tcec-chess.com/#game=13&round=fl&season=cup16
Yes, engines would almost certainly never play 2. f4. That's a different question than whether chess is solved, for which the question of interest would be "given optimal play after 1. e4 e5 2. f4 is the result a win for one side or a draw?"
replyIt's also almost certainly the case, in that I don't know why you would do it, that Stockfish given the black pieces and extensive pondering would be meaningfully better than Stockfish with a time capped move order. Most games are going to be draws so practically it would take awhile to determine this.
I'm of the view that the actual answer for chess is "It's a draw with optimal play."