Proxmox 9 was released, based on Debian 13 (Trixie), with some interesting new features.
Here are the highlights: https://pve.proxmox.com/wiki/Roadmap#Proxmox_VE_9.0
Upgrade from 8 to 9 readme: https://pve.proxmox.com/wiki/Upgrade_from_8_to_9
Known issues & breaking changes: https://pve.proxmox.com/wiki/Roadmap#9.0-known-issues
For beginners here: do not run apt upgrade!! Read the documentation on how to upgrade properly.