NextCloudPi formats HDD > how to restore

mysql: Version: 10.3.27
php: Version: 7.3.27
|NextCloudPi version|v1.35.0|
|NextCloudPi image|NextCloudPi_docker_01-20-21|
Nextcloud version

My System: asrock itx 4205, Ubuntu 20.04

I have reinstalled ubuntu after some errors. To do this, I first copied my docker containers and linux containers to the external hard drive.
My system HDD I had formatted ZFS during the installation, the external one was btrfs and apparently still is.

After the installation I installed docker, openssh-server and lxd. Then I loaded a docker container and started it per

sudo docker run -d -p 4443:4443 -p 443:443 -p 80:80 -v ncdata:/data -v /media/simon/Backup_4TB/ncp-backups:/ncp-backups --name nextcloudpi ownyourbits/nextcloudpi

Problem: Now there is only the folder “ncp-backups” on the external hard disk, it is empty. Nothing else is there. Before the reinstallation there were “lxd” and “backups” as folders on it. How can I restore them?

I don’t know what happened at all. The disk is still btrfs formatted. So no formatting could have been done during the installation. At most, it could be that the disk was mounted incorrectly by nextcloudpi (which I started with docker) and formatted again. I am grateful for any hints.

Here are a few more issues:

root@simon-itx:/home/simon# ls -lh /media/simon/Backup_4TB/
total 1,0K
drwxr-xr-x 2 root root 2 Mai 28 20:11 ncp-backups
/dev/sdb: PTUUID="6652a141-2fc1-4828-bf36-11689d4655a1" PTTYPE="gpt"
root@simon-itx:/home/simon# lsblk -f
NAME   FSTYPE     LABEL      UUID                                 FSAVAIL FSUSE% MOUNTPOINT
loop0  squashfs                                                         0   100% /snap/core18/1988
loop1  squashfs                                                         0   100% /snap/snapd/11036
loop2  squashfs                                                         0   100% /snap/gtk-common-themes/1514
loop3  squashfs                                                         0   100% /snap/gnome-3-34-1804/66
loop4  squashfs                                                         0   100% /snap/snap-store/518
loop5  squashfs                                                         0   100% /snap/lxd/20450
sda    zfs_member rpool      4857374313086611899
├─sda1 vfat                  A15E-E30D                             486,9M     5% /boot/efi
├─sda2 swap                  75f512dc-d1d4-4811-a382-702a45b0c7e3                [SWAP]
├─sda3 zfs_member bpool      1445861048992372300
└─sda4 zfs_member rpool      4857374313086611899
└─sdb1 btrfs      Backup_4TB e8cbe514-6d7f-4945-a47b-4e0d05e5417c
ROOT/ubuntu_2xoyl8/var/games               zfs       885G  128K  885G   1% /var/games
rpool/ROOT/ubuntu_2xoyl8/var/lib                 zfs       886G  929M  885G   1% /var/lib
rpool/ROOT/ubuntu_2xoyl8/usr/local               zfs       885G  128K  885G   1% /usr/local
rpool/ROOT/ubuntu_2xoyl8/srv                     zfs       885G  128K  885G   1% /srv
rpool/ROOT/ubuntu_2xoyl8/var/snap                zfs       885G  640K  885G   1% /var/snap
rpool/ROOT/ubuntu_2xoyl8/var/spool               zfs       885G  128K  885G   1% /var/spool
rpool/ROOT/ubuntu_2xoyl8/var/log                 zfs       885G  3,4M  885G   1% /var/log
rpool/ROOT/ubuntu_2xoyl8/var/mail                zfs       885G  128K  885G   1% /var/mail
rpool/ROOT/ubuntu_2xoyl8/var/www                 zfs       885G  128K  885G   1% /var/www
zfs       888G  3,5G  885G   1% /

How did you mount the drive containing the backups?