>>713931643NTA, but:
The "twist" is shown within the first hour basically. Your consciousness was downloaded into a robotic form, in which the world on the surface ended because of a meteor strike. Literal scorched earth. It's not a matter of twists really, you're given a single goal (get a collection of consciousnesses into space to that the satellite can run a paradise simulation off of solar power) and go through the existential dread/horror of reaching that end.
The only real ending "twist" is that there's a coin flip concept. That, when you upload your consciousness, you may not be the copy that gets uploaded and instead remains in the form you're in. But that's bullshit and the main character doesn't understand due to stupidity or desperation. There is no coin flip. When his consciousness gets uploaded, he remains in the dying sea base, alone, with monsters and darkness encroaching. His copy gets to live in paradise, but he remains, to simply wither away for however long his form will last.
I love the game, but the "horror" more comes from knowing that there is no good ending. There never was going to be one, even if the protagonist thought there was a chance. The only "good" is knowing others are able to live out their lives for just a bit longer.