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
As of the last update released on August 1st, the “old” VMs are now visible again. The latest Electric Eel chain also merged all Core features into Scale, so the jump should not be as drastic any longer. I’ve always lived on Scale, but I assume you could try backing up your config and spinning up a new Scale VM and restoring the backup to it. No matter how you dice it though, it will be spicy!