There used to be quite a thing for randomised conpositions in the Baroque era and later, called Musikalisches Würfelspiel.

There was also a thing around tape cut-ups in the 1950s, with William Burroughs being very into this stuff, with David Bowie later picking some of this stuff up. It was more about deconstructing expectations than creating something beautiful, but some of the material is very interesting.

For the first, see https://en.m.wikipedia.org/wiki/Musikalisches_W%C3%BCrfelspi...