"Fantasy Adventure in the Canteen"

I'm Looking for a Novel Where the Main Character Is a Genius from the Upper World. I Feel Like There Are Very Few Such Novels That Are Very Original.

Want to watch something like "The Saint is cold and kind, how can she be a villain?" (The Altar of Sin)" book. The protagonist is a genius from the top continent in the upper world. He has experienced in the lower world and can go back at any time. He belongs to the invincible stream. It is a traditional fantasy. He is invincible in the lower world. Just watch without CP.