I am looking for a novel where the MC is or gets inserted as the Villainess or Side Character of an Otome game and derails the tropes (and preferably plot) while doing so. Dragoon, Villainess turns the Hourglass, Observation log of the Villainess, stories like that. Bonuspoints if the Heroine or embodiment of the plot loses their shit while the MC does so
Ceo's villainess childhood friend - it doesn't have the otome game you're looking for but it does have transmigration to villainess. Aside from that, there's The World of Otome Games is tough for mobs - this though might be rhe the one you're looking for as it shows how "outsiders" influence the plot. But it has a male mc though.
I mentioned side characters because I don't really care about the gender of the MC. They can be a Love Interest that doesn't care about the Heroine, they can be the Villainess reborn, they can be a player/reader of the game/novel that was reincarnated, they can be the Butler of the Villainess or Heroine. They can even be a simple Baron from somewhere that tries to make the best of it and accidentally Butterfly effect the original plot into derailment because of it. As long as they subvert the original story or have a reference of how things were supposed to go and are trying to prevent that, that's all I need. The MC doesn't even have to be all that aware they're doing it, as long as the reader is.
Dare ga Otome Geemu Dato Itta! And this one's not an otome game but actually a web novel, and well.. yaoi The Reader and Protagonist Definitely Have to Be in True Love