Trying to create new backup, but can't find folder of external drive in list

I’m new to Duplicati.
Like in the title described, I want to create a new automated backup and already failing in the backup destination window, because I can’t find the folder of my external drive, where I want to store my backups on. The external drive is always hooked to the system, but the system runs on an SD card.
It should be in /mnt and be called ext/ but /mnt hasn’t anything inside it in the dropdown menu of Duplicati.

Raspberry Pi 3 B+ with
Raspbian GNU/Linux 10 (buster)
Docker 20.10.12
linuxserver/duplicati:latest Container from Dockerhub (

Since you’re using Docker, did you make sure to set up bind mount so that your container can see that area of the host machine? I’m not sure how familiar you are with Docker, but by default it has its own filesystem view that is not that of the host machine.

I will look into that, thanks for pointing me in this direction.