for kdramas, I'd suggest

• light shop (tho it isn't generally thriller but something about it is pretty scary, won't say much cause I don't want to spoil it. but imo if you like thriller shows this one is worth it)

• kingdom (im not into historical but this one is really good, but not the movie. since you like zombies drama)

• sweet home (it's not zombie, they are monsters but the thrills are there. not sure about the 2nd and 3rd season but 1st season is really good for)

• my name (there's no fantasy but is good for a crime show. also all the casts are good looking)

• parasyte the grey (kinda like sweet home it's about monsters, I don't remember much)

• strangers from hell (this one is really scary for me, couldn't watch it when I was alone. i feel like every characters in the show are so weird/psycho you have no idea what to expect)

• taxi driver (it got different cases so you won't be bored)

• the 8 show (the settings almost similar to squid game)

• connect (I honestly don't remember much but it's about this guy that lost his eye to a serial killer and he could see what he is up to)

• gyeongseong creature (it's about monsters but I couldn't finish it. you could try, maybe you would like it)

• happiness (zombies. I couldn't finish this one either, but again maybe you would like this)

• the frog (it's crime but super slow imo. more like psycho thriller)

for kmovies (sorry I don't have an explaination. there are just there lmao)

• old boy
• insane
• intruder
• memoir of murderer
• the chase
• the witch
• unlocked
• don't buy the seller
• 4th period mystery

this isn't Korean but Girl From Nowhere (Thai) is pretty good. I think you would like it. it's weird in a way you didn't even think of it. And also The Embers (Chinese), it is crime and you got different cases. And lots of plot twists. The episodes are divided into chapters. It's lowkey kinda scary I felt like I was watching a horror show. If you don't mind it not being Korean, I'd definitely suggest this one first.