Wait… different branches for different environments? Wouldn’t you run into the same problems?
I personally prefer having IaC in the same repo as the code. Any changes to the code OR the IaC uses the git flow as per normal and requires a PR. When the PR is merged to develop its pushed to QA environments automatically - therefore updating infrastructure with the updated IaC.
We update deployment configuration separately (because why would we include anything environment-specific in the repo?), this never presents any major issues although sometimes I guess you'd need to update the config just at the same time as merging the code PR which is slightly inconvenient and is somewhat OCD triggering, but its a productive setup so I don't mind.
Much fun ensues in trying to have any sense of a predictable timeline when you want to rollout any app feature requiring IaC changes.
Feels worse than on-prem datacenter work cuz at least there the team was bigger, and it was slow, but mature with a ticketing system, SLAs and no key man dependencies.
With someone-else-owns-myIaC, I am dealing with 2-3 DevOps dudes who kind of sort of use Jira sometimes, and lack staff in some of the region timezones our business operates in.