Some news for those of you running Proxmox: https://www.proxmox.com/en/about/company-details/press-releases/proxmox-virtual-environment-9-0

Upgrade guide: https://pve.proxmox.com/wiki/Upgrade_from_8_to_9 

Looks like it should be fairly seamless to upgrade in-place.

Known issues: https://pve.proxmox.com/wiki/Roadmap#9.0-known-issues