I’ve just come across this tool for building a Proxmox VE boot ISO. Builds successfully on Ubuntu 24 running on a 4 core OCI A1 Ampere based instance.
https://github.com/jiangcuo/pve-iso-builder
The developer team at Proxmox have been equivocating as to whether they should go ahead with support but the Proxmox community effort for Arm64 seems to be solid.
https://forum.proxmox.com/threads/proxmox-on-aarch64-arm64.121925/page-4#post-737710