Workflow for multi-environment management + promoting releases between environments

Developers may want different IaC for each environment (dev, test, prod).
- What is our guidance for managing that?
- How do we enable a developer to advance their app from one environment to another (e.g. dev -> prod)?

Note that using branches for management is sort of an anti-pattern/dated approach and there are developers who do not view this as an option (e.g. https://codefresh.io/blog/stop-using-branches-deploying-different-gitops-environments/)