The text specifically refers to him predicting everything as a means of survival, since life itself is ultimately a threat to him. There's an immense level of danger in life (almost anything can be lethal) and the show reinforces this as part of its core theme. It's effectively limitless, which is further supported by how he can account for highly improbable scenarios, like being trapped with a non-canonical version of himself (hence “even things he hasn’t thought of”). And the wording also emphasizes that everything quite clearly, especially by including outcomes that Rick hasn’t explicitly considered. You can't meassured this down with some finite numbers.
All of that was with an undisclosed amount of time for planning, thinking about it or not, remembering it or not.
It does not serve as basis to claiming "he's gonna solve within seconds a game with 10^120 possibilities" because the key word is
seconds, up in the fly, instantly, and similars, which this does not serve as enough evidence to prove would be a possibility in the situation he's in rn
Which is exactly why I brought up that scan in the first place. He planned for everything (including things he hasn't even thought of), so something like “playing a simple game of chess with my life on the line and still winning easily because I already accounted for it” isn't really out of reach for Rick.
If that was the case, then he wouldn't lose in checkers against Morty, which he did in canon
Also, his life isn't on the line, only if he cheats lol
If the loser were to die, i'd put that explicitly in OP
And yeah, he's overprepared for threats to his life, but nothing is indicating he's able to use this overpreparing to solve chess, nor solve it by himself, and he's losing because he doesn't use the prep correctly according to
@ShionAH (whose presence i'm missing, here)