The distinction between composition and improvisation has always been a complex topic in the discourse surrounding jazz. Some artists argue that all music begins as improvisation, and what makes it “composition” is the act of notating the ideas after you’ve played them.

Even classical composers, who are often regarded as Western music’s greatest artists, started by experimenting at the piano—testing ideas, rejecting some, playing others, and eventually settling on a melodic snippet they felt was best. They would then write it down and gradually construct a symphony or concerto from these initial fragments.

Interestingly, classical concertos often include cadenzas—flourishes at the end of a movement—that are meant to be improvised by the performer during the performance. This tradition highlights the ongoing relationship between composition and improvisation, even within formal classical music.
https://www.stereogum.com/2327057/makaya-mccraven-new-album-off-the-record/columns/ugly-beauty/