What kind of artist? I dont know about Twice but i'll speak for Blackpink.
Songwriting? All of them (Jensoo LSG, Rosé Gone, Lisa Say So Rap, Jisoo Habit, Jennie Solo Remix Rap, Sure Thing Cover).
Production (Jennie has been credited as one of the composer of LSG).
Choreography? Lisa been doing it since predebut also Say So dance break was choreographed by her.
Blackpink members are involved in deciding the concept of The Album (MV, Styling, Concept). It might not fully under their control but they have their creative input in it.
Lisa's dance performance on her YouTube channel is not choreographed by her but she has creative control for her channel. The styling, song-choice, video-concept.
Recently, Jennie has been credited as fashion editor on Vogue Korea. At the same time, Lisa is selected to join the jury for French "2021 ANDAM Fashion Awards".
Jisoo, being an actress is a part of art. Art of expression. If her acting is great, it is an art.
Lastly, wait for Rosé solo album
There are many forms of art. Be specific