PVE Adopt a Native LXD/LXC
From WikiMLT
Converting an LXD/LXC to a ProxmoxVE/LXC is pretty easy, because the aye (almost) the same thing.
1. Create a backup of the LXD/LXC container.
2. Copy the backup of an LXD/LXC container to a ProxmoxVM's template directory within its storage.
rsync --progress remote.host.name:/mnt/backups/lxc-backup.tar.gz /mnt/pve/stirage-disk/template/cache/