"can only restore from ext/btrfs filesystems"

I’m trying to setup a docker installation after messing up my non docker installation. I have a backup file without data. my instance is fine and running.
but when I try to restore the backup, that is only a few days old, I cannot restore it and I get

Running nc-restore
Can only restore from ext/btrfs filesystems

and I sincerely don’t know what to do. I’ve succesfully restored the backup using

mysql -u root nextcloud < nextcloud-sqlbkp_xxxxxx.bak

as mentioned in other topics, but the entirety of the backup cannot be restored.
if possible I could also restore everything manually, just following some documentation about permisisons and what to be put where, but I could’t find any.
also, as far as I know, the data folder inside the nextcloud one should contained one folder for each user, but this is not the case, is it possible that the backup wasn’t done properly?

Maybe this can help:

I have replied to that topic, I’ll wait for an answer from him on how he got it to work and I’ll give it a try.

apparently the backup gets restored if the backup is put in /data/ inside the container

I am having the exact same issue.

pi@nextcloudpi:~ $ sudo ncp-restore /media/nc-backup/nextcloud-bkp_20200125_1579974342.tar.gz
Can only restore from ext/btrfs filesystems

Also if I try to restore from within the “data”-folder you mentioned, I get an error:

pi@nextcloudpi:~ $ sudo ncp-restore /var/www/nextcloud/data/admin/files/nextcloud-bkp_20200125_1579974342.tar.gz
Refusing to restore from /var/www/nextcloud

Any help appreciated! @DystopianLphant, did you manage to solve this?