Yes path does exist Taifun... see post #8. Created it with a file in the ADS.
Also tried with Pictures Folder. Yuk. The path works for Image and Label but not CloudDB. Image is Created from a Canvas saved in ASD and moved to Shared folder. Why CloudDB does not respond. Image and path created by the app?
Here is a test app.
ShareCanvasCloud3.aia (1.8 MB)
file should show up in your Shared folder but will not load into CloudDB
In your Screenshots you are using
file:///storage/emulated/0/Shared as directory...
This directory is not accessible...
See also the overview by @Anke here Some basics on Android storage system - #34 by Anke
Try shared storage like /Pictures or /Download or the ASD. ..
Taifun
Storing a FILE from the ASD to CloudDB works just fine, testing with companion app, the file....
file:///storage/emulated/0/Android/data/edu.mit.appinventor.aicompanion3/files/hsqre1.jpg
returns
/storage/emulated/0/Android/data/edu.mit.appinventor.aicompanion3/files/AppInventorBinaries/BinFile5014095958271272784.jpg
from cloudDB
yes it is accessible.
tried Pictures ... same response.
Thanks @TIMAI2 . Perhaps that happens when you use the Linux Companion. Perhaps the problem is my image is sourced by the Canvas and you are sourcing by an image.png ?
Using Anke's as a guide:
I still cannot populate the CloudDB. Going to read a book.
Correct (at least not on Android 11+).
No, not on Android 11+ as @Taifun already said and you can see in my guide:
EDIT: Yes, there seems to be an issue/bugug with this if you set the DefaultFileScope to Legacy or Shared on Android 11+.
Thanks Anke for your comments. I am testing on an Android 8.1 and an Android 11 and am still lost. 
Note on Android 11+:
If you unistall the app without deleting the image beforehand (or tested with Companion before), you must change the filename of the image, because then the new installed app is another app that cannot access the old file (stored by the previous app version).
This is one of the many pitfalls of this ("idiotic") new Android file system. 
Trapped in this pit. Thank you so much for your help. Testing on 11 right now and and things not working as expected. I will try an 8.1 cell in the morning. Thanks.
What is not working as expected?
Not displaying the CloudDB on an Image control.
My screenshots are from a Pixel 2XL (Android 11), tested with the APK & Companion.
Post the blocks ... (or did you try my aia?)
Label1 shows the value of the CloudDB.GotValue:
Yes I tested, 
It is working now (I think) after I disabled Canvas1.Clear. I do not know why. Now I see the Image controls showing the canvas was sent to CloudDB and retrieved. Thanks again.
Will test on 8.1 Android in the morning.
This has nothing to do with Linux....
?? really - I have found it will only save an image using a full path: file:///...../image.png
My blocks are above, for Android 10 & 12 using companion app. This stores returned cloudDB files in the ASD/files/AppInventorBinaries.
Your blocks show that AppInventorBinaries needs to be created in root? is this for android <10 ?
CloudDB, in its current form, does not appear to automatically create the folder AppInventorBinaries
