@Manhwa_Void do you mean “sleepy princess in the demon castle”?
If so I love this series so much that I even bought some manga of it to read before going to sleep.
Manhuas for the smart protagonists
https://mangabuddy.com/manga-list/218314
And this one for underrated gems(Recommend to read
https://mangabuddy.com/manga-list/218314
And this one for underrated gems(Recommend to read