Thanks for the suggestion! I tried to do that and have the files reside on a mount (on my NAS) but that didn't work, resulted in a "chmod" error. So, instead I've created a shell script that runs every night and creates a backup & copies the resulting zip file to my NAS :)

By the way, when using docker volumes, you can see the actual files as well. In my case (RPI4) they are located here: /var/lib/docker/volumes/paperless_media/_data/documents