What have I done wrong?
You are using a tutorial from 3 years ago that claims it only worked on Raspbian / RetroPie, at no time does the tutorial say it is compatible with Recalbox.
I'm not a developer, and I can't tell if the script is compatible or not, I can't test it, nor do I have enough technical knowledge to help you with that.
Maybe this will help you:
https://recalbox.gitbook.io/documentation/v/francais/tutoriels/systeme/modification/ajouter-votre-propre-script-au-demarrage