Both dramas feature son traveling back in time to when his parents were young and changing the past to make his mother's future happier. Both also feature the mothers best friend and the son to have a close connection

Drama adaptation of novels by the same author
Youth Romance
School life romance going into adulthood

Popular and cold male lead who secretly like the FL and helps her to get better grades etc. Jealous of other male friends. Starts in high-school and ends in adulthood.

Co-Habitation
Genious Cold-Male Lead who treats the FL warmly
Plus there's one scene that is a copy of each other. (Not gonna spoil which one)

A sweet love story with a boss and employee. The ML falls in love with the FL only and rejects other women. With the FL, he is warm, happy, and amused whereas with the others he is cold and unapproachable. The FL is a sweet and naive girl who is lost in thinking and imagining things. The ML also chases after the FL.

Both have 2 personalties. With the other personality a sweet, kind, gentle person and the original personality a cold, ruthless person. But on SHNPT there is reincarnation, supernatural elements added.
Both have a previous connection with the FL with the other (sweet) personality. They both also have the second personality getting closer to the female lead and them bonding while the original personality does not like the FL at first. There's also cohabitation between the ML and FL due to FL safety.
All in all, I feel, that HKM is a much simpler remake of SHNPT with some plot changes according to their culture and audience preference.

Both have daughters that go missing/kidnapped from wealthy families and are raised by poor parents. Both find their real parents after 20 or so years. Both are about forgiveness and redemption.

Similar in terms of face blindness by a main lead which leads them unable to differentiates between two aspects of the same person. They (person with the face blindness) starts to love the second identity of the main lead. Also face blindness starts to get cured with their love for each other.

Both are similar. A genius chef (ML) and a food show producer/writer/host (FL). The FL does anything and everything for the ML to come to the show and both gradually falls in love with each other.

In both, the girl dies in the present time and gets sent back in historical time into the body of a noble girl. In both, the prince then falls in love with the girl.

Both are about a divorce lawyer and a matchmaker. Their office's are opposite one another. The ML falls in love first. They get together to matchmake divorced and lonely couples.