Heroku is not gigalixir and things might be different.

As I said already, once you understand how to deploy without CI/CD it should be trivial to implement in any CI/CD pipeline.

But to do this, you need to understand manual steps first, you’ll gain nothing from a premade CI file that doesn’t suite your needs or is underdocumented and you miss important variables in the pipeline.

Personally I use gitlab ci a lot, for work and personally. At the office I’m called “the deployveloper” because I always find some way to deploy from gitlab. And this is easiest when starting from a fresh VM and recreating and reinstalling the necessary toolchain from scratch and understanding what’s going on.