When using PVE in a cluster setup, /etc is no longer purely a single filesystem. PVE uses FUSE/corosync to share /etc/pve across the cluster, and you can’t just copy it like any other directory.
I can only provide limited advice since it’s been a while since I last touched Ceph, but if the OSDs haven’t been overwritten then you should be able to recreate the cluster. CephFS, I’m not quite so sure. The recovery steps in this post might be helpful, but I’m sure you’ll probably get better advice sometime later on your own thread on the PVE forums.