Yeah, that was said in the lore card about the flower game.
A computer can simulate the Flower Game, explaining how the Vex are able to simulate possibilities. It’s unknown if the Forest exists in the field or just within the Vex Network.
The Vex existed in the Garden for a long long time, they are unique as they are the only non paracausal race to remember their time in the Garden and likely able to use that experience to help them in the material universe.
As for Panoptes, it isn’t figuring out Dark and Light, it’s maneuvering us to kill each other off.
That’s why the future only changes when Guardians do something. The Vex are bidding their time for both sides to fight and weaken each other, then they will strike.
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Actually, Panoptes became a problem once the Traveler awakened, and Panoptes became able to "see" Sagira's Light. In other words, Panoptes was coming close to understanding the Light, which was why he abducted Sagira, and why the future it was going to direct the Vex towards would have inevitably led to the destruction of both the Light and the Dark, likely because Panoptes was about to figure out how to 'simulate' Light and Darkness. It's not that the future only changes when Guardians do something; it is that the Vex take notice whenever Guardians do something, as happened at the beginning of Season of Dawn. When the Undying Mind was destroyed, the simulations with the Infinite Forest changed to predict a future where all of reality was subatomically annihilated by the Darkness, with a Pyramid ship floating over the remains of the Traveler and the Last City. The Vex's plans could involve waiting for both sides to weaken each other, but the Vex of the Black Garden actively pursued the power of Darkness.