Use Veeam Agents to backup your Nutanix VMs.

Then create an empty VM in Proxmox and use the recovery media to do a bare metal restore.

https://helpcenter.veeam.com/docs/agentforwindows/userguide/howto_baremetal_recovery.html?ver=50
 

Windows should work without big problems. Linux VMs can work too but sometimes they have issues in such restores.

Best regards

Fabian

As @Mildur said, in your case you need to use Veeam Agents. Veeam Backup & Replication doesn’t interact directly with the Proxmox hypervisor.

Only VMmware vShere, Microsoft Hyperv and Nutanix Acropolis are compatible nowadays.

I would just say up front that I may be somewhat of a VMware snob and don’t have any Proxmox experience, but I would not be using Proxmox in a business environment.  I don’t believe that it’s a mature enough product for mission critical workloads.  Honestly, as much as a dislike Hyper-V, I’d probably be looking at a well-built Hyper-V cluster before Proxmox, but VMware would easily by my top choice.  If you’re fine with being an early adopter, then perhaps Proxmox is an okay choice, but I would prefer more well-baked applications.

As for you question, as noted above, Veeam does not have integrations with Proxmox, so you’d be looking at agent backups and “bare-metal” restores.