Cinderella no Giri Ane ni Tensei Shita kedo Futari no Ouji ni Dekiaisareteimasu

Reincarnated as the wicked stepsister in the fairy tale Cinderella, Atra is sick and tired of her life as described in the story. Finally, on the night of the ball, a shocking revelation: Cinderella's true identity is a man! At that moment, her life is turned 180 degrees into becoming “the love interest”! An impossible isekai fantasy love-triangle!

(Source: Manga Park, translated)