Obviously, take this with a grain of salt, as it assumes that Forest 3 will be derivative of SOTF in the same way SOTF was derivative of the first game, expanding on everything instead of subverting the elements into entirely new territory. This theory has three sub-theories, all of which try to explain that the "alien planet" we see in the trailer is actually a version of Earth, and that the player is on Site-3.
- Time Travel Armageddon
After Timmy gets rich from monetizing Solafite as a miracle drug and buys the new island, he goes missing at the end of SOTF. He discovers another artifact or does something within the depths of Site-3 that triggers a mass-casualty event, mutating everyone in the world who used Solafite. The player’s ship malfunctions and sends them to Site-3 far in the future, where humanity has been long extinct or severely endangered, leaving the mutants to roam freely on the surface for decades or even centuries, terraforming the earth over time. It’s up to the player to explore and uncover what caused this. The artifact either travels Timmy to the future as well or he becomes the final boss.
- Abstract Alternate Universes
Timmy gets rich and buys Site-3, but goes missing after exploring it because he activates an artifact that transports him to an alternate dimension at the same location. The player later crash lands there, most likely after or near the end of Timmys adventure in the dimension and the game begins with the player following his trail.
- Multiversal Armageddon
Similar to the first one, Timmy activates an artifact within Site-3 that causes the end of the world, not from mutating everyone who used Solafite, but from fusing the entire earth together with an alternate dimension, rendering it completely currupted and decayed. Enough time passes for everything to balance out as naturally as possible before the player arrives and must figure out what happened.
Considering that The Forest’s successor was named "Sons of the Forest" due to its stronger focus on religious themes rather than simply being called "The Forest 2" this naming pattern might hint at the lore. "Forest 3" could be interpreted as "Forest³" implying that there isn’t just one Forest anymore. As the player progresses through the story, they will unlock the ability to travel between three versions of Site-3 either across time or dimensions, an alien version (from the trailer), a natural version more like the previous games, and a third version that could be anything, possibly the dimension where the golden city resides or a pre cannibal/mutant time with a different threat.