No 3rd gen idol group member had a huge hit with a solo song that reached the level of legendary of :
- Eyes, nose, lips, Ringa linga - Taeyang
- Crooked - GD
- Bubble pop - Hyuna (her whole discography tbh)
- You & I, Don't cry - Park Bom
- Gashina, 24 hours - Sunmi
- Move - Taemin
- Fine, I - Taeyeon
I'm not talking about numbers and success, I'm talking about a song that a random korean person and their mother would know and sing along.
The only other song that has come close yet not reached the level is Solo by Jennie. The other bp members and bts and exo members have released many successful songs but their popularity is limited in the kpop fandom sometimes in their own fandom. Other honorable mentions are Maria by Hwasa and Fiancé by Mino, but they're still very far away from the goal.