Roadmap - Proxmox VE
https://pve.proxmox.com/wiki/RoadmapQEMU guests: The migration protocol for sending the Spice ticket changed in Proxmox VE 6.1. The code for backwards compatibility has now been dropped, prohibiting the migration of VMs from Proxmox VE 7.0 to hypervisors running Proxmox VE 6.1 and older. Always upgrade to the latest Proxmox VE 6.4, before starting the upgrade to Proxmox VE 7.
Upgrade from 6.x to 7.0 - Proxmox VE
https://pve.proxmox.com/wiki/Upgrade_from_6.x_to_7.0The ifupdown2 package, which Proxmox ships in the Proxmox VE 7.x repository, was adapted with a new policy configuration, so that it always derives the MAC address from the bridge port. If you're already using ifupdown2 with Proxmox VE 6.4, and you upgrade to Proxmox VE 7.x, the ifupdown2 version 3.1.0-1+pmx1 (or newer) will ensure that you do not need to adapt anything …