The systemd unit ceph-volume@.service activates the local OSDs. To do that it needs the ceph.conf.
On Proxmox nodes /etc/ceph/ceph.conf is a symlink to /etc/pve/ceph.conf and therefor only available after pve-cluster.service is running.
Please add a ceph-after-pve-cluster.conf into /lib/systemd/system/ceph-volume@.service.d like with the other Ceph service units in the pve-manager package.
On Proxmox nodes /etc/ceph/ceph.conf is a symlink to /etc/pve/ceph.conf and therefor only available after pve-cluster.service is running.
Please add a ceph-after-pve-cluster.conf into /lib/systemd/system/ceph-volume@.service.d like with the other Ceph service units in the pve-manager package.