Seperate Proxmox node from cluster
In order to separate Proxmox node from cluster:
systemctl stop pve-cluster
systemctl stop corosync
pmxcfs -l
rm /etc/pve/corosync.conf
rm -r /etc/corosync/*
killall pmxcfs
systemctl start pve-cluster
pvecm expected 1
rm /var/lib/corosync/*