@loudlemur On Cloudron, apps are run in containers. The paths which are mentioned in app docs and messages are inside the container. They are not easily found on the server (and not meant to be directly edited by ssh'ing).
/app/data is the path in the container where apps write to. The easiest way to access this is using the File manager. The file manager exposes only the /app/data directory of the container and nothing else.
If you want to see the full container file system, you have to use the Web Terminal. You can always cd into /app/data there as well. There you will see the same files as the file manager.