Raspberry pi clusters?
Unfortunately no, check the FAQ. Seems to be working for some AI chips only
Q: Can I run Proxmox VE on a Raspberry Pi or a similar single-board computer?
A: No. An arm64 host must boot through UEFI and describe its hardware through ACPI. Device-tree-only boards and legacy boot are not supported.
I've been running a fork called PXVIRT on my Pi. Though I'm sure you could probably still install Proxmox on top of Debian and have it work.
Proxmox
Proxmox VE is a complete, open-source server management platform for enterprise virtualization. It tightly integrates the KVM hypervisor and Linux Containers (LXC), software-defined storage and networking functionality, on a single platform. With the integrated web-based user interface you can manage VMs and containers, high availability for clusters, or the integrated disaster recovery tools with ease.