This buildpack enables use of pnpm on heroku.
heroku buildpaks:set https://github.com/unfold/heroku-buildpack-pnpmThe buildpack will install node and npm into the environment. It will read the package.json file to get the NPM version to use (defaults to version 16).
You should remove the default heroku/node buildpack. Else it will do a double-install of dependencies etc.
You need to create a Procfile in the root of your repository containing web: npm run start if you do not already have one.