Does smut stuff happen in this manga ?

Yes, but it's mostly implied.
I think there's like 1 chapter with the main couple showing the foreplay and then some scenes of them having sex but nothing explicit tbh. Most of the time there's a scene of them getting horny and then it skips to the next day with them on the bed sleeping or sth.
Honestly this manhwa is heavy plot wise, so they don't even focus that much on the romance, let alone the sexy stuff haha

Oh okayyy. Thxs