RESOLVED: (1) with only Nodejs Buildpack installed, getting error referenced in question, (2) Added Ruby Buildpack, as suggested, (2) git push successful, however git push heroku main failed with errors about yarn installation and suggestion that I add an empty yarn.lock file, which I did, [ An aside / FYI, the fail re the yarn installation's location led me to this thread, however, it wasn't the issue: https://github.com/yarnpkg/berry/issues/5380 ], (3) git push successful, however git push heroku main failed because I had a package-lock.json & a yarn.lock file. Here is the obscure Heroku help page that resolved it: https://help.heroku.com/0KU2EM53/why-is-my-node-js-build-failing-because-of-conflicting-lock-files After removing the package-lock.json file and adding it to .gitignore, my Heroku build is successful and deploys correctly. Bottom-line: Conflicting package.json and yarn lock file, NOT a ruby issue.