I have a "postinstall": "patch-package" in my scripts within my package.json.
since I must patch a npm package.
It of course works locally but when I deploy to fly.io using github actions then I’m not quite sure where deploy.yml I should be calling the postinstall
That looks like a github workflow… that won’t normally affect what is deployed. Typically you would want to look at a Dockerfile to control what is deployed at fly.io.
Also, postinstall is automatically run by npm install. See: scripts | npm Docs