Going back to the shell command, I get this on Android 9, I imagine that on Android > 9 it will not be so easy to explore the files.
Everything in MIT Companion.
When ListDirectory.Private (/storage/emulated/0/AppInventor/data) I get a series of files, I don't know if they are files from previous versions of MIT Companion that remain in that directory.
There is a cache in
/data/user/0/edu.mit.appinventor.aicompanion3/cache
another
file:///storage/emulated/0/Android/data/edu.mit.appinventor.aicompanion3/cache
TinyDB in
/data/user/0/edu.mit.appinventor.aicompanion3/shared_prefs/TinyDB1.xml
It's good to know what's out there, but I am shooting for an extension-free solution, so I can post to the Gallery and hope for eventual cross-platform compatibility.