I love ballad and RnB singers so they may not be that popular internationally but in S-Korea some of them are more well known.
Huh Gak: Only You
CAR, THE GARDEN: Gimme Love
hyukoh: Basically every song from them but my favorite of all time is Die Alone
offonoff: Bath, Cigarette.
The Black Skirts: Who do you love (seriously everyone needs to listen to this song it's so beautiful)
JANG DEOK CHEOL: Good Old Days (i cry almost everytime i hear this song)
But ofc i love 'nugu' kpop artists and bands also, Im a big fan of N.Flying, A.C.E and Day6.