Cinderella no Ane desu ga, Fuhoni nagara Ouji to Kekkon suru Kto ni Narimashita: Migawari Outaishihi wa Rikyuu de Slow Life wo Mankitsu suru

Adelina, Cinderella's stepsister, is forced into marriage with the nation's beloved "handsome prince" after Cinderella elopes with a wizard instead of accepting his proposal. Though the prince declares, "Even if we marry, I will never love you," Adelina has no objections! He's free to have mistresses or concubines—she plans to live as a figurehead princess, enjoying a laid-back royal NEET life in a remote palace surrounded by fluffy companions. However, as she pursues her goal of a peaceful life and an amicable divorce (with a generous settlement), the once-distant prince starts to take an interest in her...!?

(Source: Futabasha, translated)