Veeam Backup and Recovery supports Proxmox as of 28 Aug 2024

https://www.veeam.com/blog/backup-replication-community-edition-features-description.html

Veeam Community Edition, only works with VMware, HyperV and AHV. To use Veeam with Proxmox, you need a License.

https://www.veeam.com/products/free/backup-recovery.html

Veeam Backup & Replication Community Edition is the backup software to safely secure virtual, physical, and cloud workloads. It protects up to 10 workloads, including Proxmox VE, VMware, Hyper-V, Windows and Linux servers, laptops, NAS, and more.