I think I am not the only one who wonder where those files hiding, so I hope this information helps:

When you start X-terminal the default path is:
/home/user/
When you start some Maemo apps (example Hamster Filer):
/home/user/MyDocs/
But by default it does not show hidden paths (names starting with dot) that shown some another Maemo apps and they show that MyDocs folder as the most up level of path (example LeafPad), so documents-folder showing in LeafPad is actually:
/home/user/MyDocs/.documents/
In MyDocs folder there is .images and .videos folders too.

If you use Maemo apps (downloaded with Application Manager} then it might show only up to MyDocs folder and use example /home/user/MyDocs/.images/ folder.
If you use Devuan(/Debian) apps (downloaded with apt-get command) they use example /home/user/Pictures folder by default. You can go to to MyDocs folder, but you might not see hidden folders inside it, when you use file-selector.

You don't mix Maemo app and Devuan app files easily, that sounds good, BUT...quite soon you want do that until the best Devuan apps are converted to Maemo apps. And how to open file directly from USB-stick with Maemo app? So I think better make changes to Maemo file-selector and/or default folders.