[SOLVED] mix cluster proxmox ve 6 and 7 version

The "solved" prefix is already set... but I assume that was an accident.

can you mix the cluster proxmox ve version 6x and 7x ?
Only during the upgrade window. Make sure to get every node to the same version as soon as possible.

Live migrations from older to newer versions are supported and should always work. Live migrations from newer to older can work but are not guaranteed.
Additionally, depending on which node you access the GUI, it might be missing new features or will run into errors because the newer GUI expects API endpoints that are not yet present on older nodes.