Change data destination via GUI

I received recently a Nextcloud box. I wanted it to work with RPi 3 and have installed Nextcloud following this guide. This works nice so far:

All seems to work well and my data appears in the webinterface. However, when I go to /media/data folder via SSH (as per the guide) I was expecting to find all my data there. Instead I only found a lost+found folder.

Can someone point me to the real location of the data? And how can I ensure my data ends up at my /media/data drive

The path to your data folder is in config.php

I found the file in /var/snap/nextcloud/current/ directory. However, do you have to change the path here? I have been assuming this is what ‘external storage’ was for and I added the mount point there (see screenshot below). However it does not seem to write the data to the /media/data folder but rather to the default folder specified in config.php