The Star Wars Jedi: Fallen Order Dark Side options work like this: they don't. There aren't any. This is the single-player Star Wars adventure that fans have waited years for, but developer Respawn Entertainment is making no excuses about dropping one of the common features for story-driven Star Wars games: the choice of whether you want to be a kind and selfless Jedi, or a vengeful, lightning-blasting wielder of the Dark Side.
Respawn Entertainment confirmed the decision on the EA E3 2019 stage. Because they worked with Lucasfilm on Star Wars Jedi: Fallen Order's story, that means its events are part of modern Star Wars canon; characters that appear in the game are "all gonna live in other places" as gameplay director Stig Asmussen explained. That goes for folks we already know, like Star Wars: Rogue One's Saw Gerrera as well as newbies like Cal Kestis, and it comes with some canonical obligations.
"It goes back to the fact that Cal's authentic and he has to fill a certain role so he can be used in other places," Asmussen explained. Then Respawn Entertainment boss Vince Zampella sealed off any more potential Dark Side speculation with five words: "This is a Jedi story."
That means you probably won't run into any QTEs where you have to decide whether to kill an enemy or spare them, or any skill trees to help Cal shoot better lightning from his fingertips. It could be fun exploring the Dark Side in the Jedi Knight or Knights of the Old Republic games, but if Respawn Entertainment and Lucasfilm have one story they want to tell on the Light Side of the Force, I can't blame them for sticking with it.