The answer is that yes you can store images/otherfiles in cloudDB, you have to ensure that you provide a full path to the file for the image to be stored. (cloudDB actually carries out a base64 conversion to store the image as a string)
See example blocks when running companion app on Android 10/11 getting an image from assets and storing it to cloud DB.
When you call back an image from cloudDB, a new file is created and stored in a folder called AppInventorBinaries.
(note, at time of writing, there is a small bug, multiple copies of the file with slightly different filenames may be stored)