as far as i know there are korean culture that i know that you must take a note:
1. if someone ask to eat ramyun at their home/apartments, in korean culture it's like flirting or invitation for a s*x
2. When drinking alcohol with older people, we have to pour, and we are not allowed to pour soju ourselves, so we pour for each other. The older person can pour whenever he wants, but the younger person need to wait or need to ask if they want more or no. And when you want to pour drinks, use with two hands and turn away when drinking with elders.
if you are not drinking with someone older, then you can drink casually, but again, the culture is to pour soju each other
3. Korean always eat kimchi while eating, for them it is like eat with chili sauce, and when eating they has a lot of complementary so it's like 4 healthy 5 perfect, So they never eat just one menu, unless it's the end of the month and finances are low, usually they only eat rice with eggs and kimchi.
4. Every time there is a K-pop event before the modern dancers appear, they usually use and show traditional Korean dancers (wearing traditional Korean hanbok clothes from the Joseon era) as the opening. This seems to implicitly convey that even though Korea is modern, they will not forget their own culture.
5. Korean and Japanese had issues in the past, because Japan once tried to colonize Korea, that's why their diplomatic relations were (untill now) are bad.
6. The global popularity of K-pop, K-dramas, and Korean movies, known as the "Korean Wave" or "Hallyu,"
7. you can't say someone older using a name. they use unnie (younger girl to older girl), noona (younger boy to older girl), oppa (younger girl to older boy), hyung (young boy to older boy), ahjusshi (to someone over 30 and an uncle), ahjuma (to someone over 30 and an auntie),
seonba/hubae/seonbanim (are terms used in schools, it only applies to fellow teacher and workplaces to indicate seniority and experience level)
in korean eventhought You call a stranger, and you don't know their age, it would be more polite if you assume they are older than you
8. In Korea, you don’t hug, you bow (to older or in formal occasion)/wave (to fellow friend) while greeting someone. Hugging is reserved for couples and close friends or family. Korea known for its introverted citizen and strong patriarchy. Most Koreans are also racist towards foreigners, they feel that native Koreans are more beautiful than foreigners, that's why Idols who are of mixed or foreign blood are often bullied.
9. A lot of korean struggling speak english, only in Busan and Seoul (big city) who their citizen more fluent in speaking english than korean in countryside (Hongdae, Jeju island etc)
10. Since childhood until they graduate from college, Korean people have the habit of studying until night (so after school they usually have a tutoring place, especially when high school exams are close, they will be more active), Usually their highest target is to study at Seoul National University (SNU)
the rest, you can read this
https://www.torntackies.com/life-in-korea-cons/
https://www.ciee.org/go-abroad/college-study-abroad/blog/20-tips-korean-culture-foreigners
https://english.seoul.go.kr/service/amusement/traditional-culture/1-overview-of-traditional-culture/
https://www.reddit.com/r/korea/comments/79tdg5/what_aspects_of_korean_culture_were_a_surprise_to/