proxmox is using KVM for virtualization and Linux Containers (LXC) for the containers. I agree that something like terraform and/or ansible would make more sense for an IAC (infrastructure as code) deployment. Most of the people I talk to that use proxmox for a homelab prefer to do things manually and don't bother with any IAC implementation.
For work I'm a firm believer in reproducible environments and IAC. We actually a combination of vagrant, libvirt, and KVM to spin up local clusters for quick testing and development. It works out pretty well, but in my homelab I don't have anything complicated enough to bother setting up terraform/ansible for. Although I imagine if my server crashed I probably wouldn't think that way anymore.
Given enough appetite and love from me, I've got a pretty robust Ansible script for building a Proxmox host with $i++ LxC's.
It's not suitable for open sourcing yet (embedded secrets and the like), but if the community wants it, it's pretty solid.
Only issue I see is the Ansible script currently always expects to be building a cluster of Proxmox hosts. I'd need to make some change to customise it so it can build out just one node though.
I've been using it or ~3 years now for my Proxmox cluster home lab which predominantly hosts LLAMA, *Arr stack, deluge, Nginx, Tailscale and a few other services.
It's not quite a one click deployment, but it can build our an entire cluster in 30 minutes after an initial Proxmox install is completed.
If you want to manage VMs, then you're probably using terraform + provider. However, SDN (Software Defined Networking) is not yet supported [1], which makes any kind of deployment with network separation not feasible (using IAC only).
For work I'm a firm believer in reproducible environments and IAC. We actually a combination of vagrant, libvirt, and KVM to spin up local clusters for quick testing and development. It works out pretty well, but in my homelab I don't have anything complicated enough to bother setting up terraform/ansible for. Although I imagine if my server crashed I probably wouldn't think that way anymore.