[nextcloudpi] Backup a docker instance


I am a new user and I hope this is the right place for my question, if not I will be glad to ask somwhere better.

I run nextcloudpi with nextcloud version 13.0.4 as a docker container on a raspberry pi, currently only privately for me. I would like to make backups of the data stored and the docker container (nextcloudpi instance).

The tool nc-backup seems only to be able to create a backup inside the docker container.

My question is, is there a way to create the backups outside of the container?
What is the way to go, to make backups in this case?

I hope one of you can help me. Please excuse me for my bad english, and if this is question was asked before.