There never was a 8.1.4 ISO. Proxmox is intended as a rolling release; you're not supposed to stay on an old version (which has known bugs). Install new nodes with PVE 8.3 and update that and your other nodes (one at a time) to the latest version. You can always migrate VMs from 8.1 to 8.3 (but maybe not the other way around).
EDIT: 8.3 is the latest, not 8.2.