Haven't used Terraform - ARM templates have a workable (though not elegant) expression system where you can use parameters to resolve stuff - so you indeed have

Haven't used Terraform - ARM templates have a workable (though not elegant) expression system where you can use parameters to resolve stuff - so you indeed have one IaC definition and use your CI/CD to set parameter values and therefore setup whatever is needed for different environments. So your CI/CD knows about the envs and not the IaC code. As it should be I think.