You click on the 'Sex' heading, and then go to the option saying 'Gender'. It gives you a quick rundown of the topic, reading: "Aside from a tiny proportion of people, humans are born either male (with XY chromosomes) or female (with XX chromosomes) and have a random but just about even chance of being one gender or the other. Some people identify differently from the gender they're born into, either identifying with the opposite gender or outside of male or female, but without any outside changes like hormone therapy or sexual reassignment surgery, they will exist in their birth gender for their whole life."
Maybe it's just something about the app, but reading this gets you thinking about gender. You've always felt like you're a guy, but you can't say you've never wondered what it's like to be a girl, plus you're kind of unsure about your sexuality. You know you like girls, but you do sometimes see men and perk your eyes up.
You start considering ways you could use this app to change how gender works. After all, there's a 'Revert' button that you can use to reset reality if anything goes weird. You could make gender fluid so people can change it at will. You could swap it round so everyone who's currently male becomes female and everyone female becomes male. You could make more genders than just male and female genders that people are born into. You could make the male and female genders work differently. You could make everyone the same gender. Your head is flooding with ideas, but eventually you work out one you want to settle on...