I wonder if Nam Gyung Min specializes in this type. Two I'm sure would fit with your ask:
- Beautiful Gong Shim : He seems like a deadbeat but is actually full of surprises: ace lawyer, badass fighter with almost superhuman skills, and more.
- Good manager: he looks and acts like a goof but is more than meets the eyes.
Other dramas:
-Flower of Evil: Both the ML AND the FL's best friend and sunbae are like that. It actually hit me with the sunbae, he's always acting like a goof but he's actually a great detective.
-Cheese in the trap : both male leads have surprising qualities (the bum turns out to be a prodigy, and the pampered rich kid turns out to be more of a thug than you'd imagine).
- Liar Game: I'll say no more
-The spies who loved me