With two Proxmox nodes, losing either one leaves the survivor with one vote out of two, so it loses quorum and /etc/pve goes read-only. Here is how a QDevice adds a third vote without a third server, plus the Wi-Fi trap and the emergency lever.

Disclosure: this is my own article (Charles Hartmann, Homelab the Right Way). Written with AI help and edited by me; the setup described is mine (Proxmox, OPNsense, Home Assistant at home). Happy to answer questions about QDevice setups here.