Written music is a “to-do” list, typically serially activated,while operating on multiple channels (parallel).
The language of written music is imperative. “Do”. “Do this” “Do Thus”. Or in some jazz compositions they may be looser instructions more akin to guidelines with freer and freer range of interpretation but are also imperatives. Just nicer.
Music does not exist until it is performed. It may be performed in the mind or on an instrument.
However, there is a written set of instructions we ALSO call music. It is in the same class as a computer program.
So yes. “the program does not exist until it is performed in / by a machine”.
The machine can be the mind performing the steps. It does not have to be a computer or a piano.