Boukun wo Migomoru Yami Ochi Seijo ni Narimashita

Our reader is reincarnated as Serena, a saintess in a novel who's destined to be treated like a villainess, give birth to a tyrant, and get executed for it. When the royal family accuses her of being an imposter, she must demonstrate her power as a saintess to survive. But once she does, she's trapped by the manipulative king and becomes a political prize for the two princes fighting for the throne. Although they were both responsible for Serena's death in the novel, the new Serena must choose one of them as an ally if she wishes to live... (Source: Tappytoon)