Gemina by Amie Kaufman and Jay Kristoff, which is described on its cover as "The sequel to the New York Times bestseller Illuminae." I would call it more of a companion book, myself. It takes place in the world of Illuminae on the space station the characters from Illuminae are headed for. But we have different characters fighting for their lives now. Sort of.
The Gemina story is told with documents, just as it was in Illuminae. There's another heroic, thrilling female character with a witty, male, love interest. Most of the time they are struggling separately, just as the couple in Illuminae did. And there's a medical-type problem to deal with just as there was in Illuminae. Something happens at one point that seems an insurmountable disaster, and then it's surmounted. Just like in Illuminae.
I'm not complaining. I've tried to repeat early successes with later books, myself. I like the set-up in these two and look forward to reading the third book in the series. I'm going to be recommending Gemina to, and maybe buying it for, my niece, who is also an Illuminae fan. I'm just sayin' the first two books' central characters are strikingly similar, as are the books' format and story frame.
Actually, I'll be kind of disappointed if the author doesn't repeat the formula with the third book.