Remove a Node from Proxmox Cluster

Check nodes

pvecm status
pvecm nodes

Delete node

pvecm delnode {node}

Check if delete node success

pvecm nodes

Remove node’s data

rm -rf /etc/pve/nodes/{node}

Remove node SSH key

vim /etc/pve/priv/authorized_keys 
vim /etc/pve/priv/known_hosts

Ref. https://pve.proxmox.com/pve-docs/chapter-pvecm.html#_remove_a_cluster_node