terraform-provider-flux VS helm-operator

IMO, a better approach would be to provision your cluster using terraform, then do cluster operations using a GitOps tool, such as GitOps Toolkit (Flux v2) - https://toolkit.fluxcd.io/. You can point multiple clusters to the same repo and they are going to apply and reconcile the desired state for all or your clusters if needed. There’s also a Flux terraform provider - https://github.com/fluxcd/terraform-provider-flux, bootstrap flux then let it do its job.

You could try this: https://github.com/fluxcd/terraform-provider-flux

You can store the values file of the helm in your repository and deploy with CI, but I personally prefer going to GitOps and Helm Operator (https://github.com/fluxcd/helm-operator) Or you can have a mixed approach where you define your HelmRelease to be deployed for HelmOperator and deploy it with CI (instead of having an operator in the cluster to apply every change in the repo)

Nothing prevents you from making an operator that creates Deployment/Services/Ingress for you.

This is even simplified with Helm (to template your resources) and the HelmOperator[1].

[1] - https://github.com/fluxcd/helm-operator

I think you should check out flux and flux helm operator. https://github.com/fluxcd/helm-operator/stargazers

fluxcd/helm-operator (Go): The Flux Helm Operator, for declarative Helming