In "download", I have a folder "storage scopes".
And in this folder, I make a folder for each application:
Download>Storage scopes>Standard notes
Each application has access only to its own directory : in the settings, I give the storage access to the last directory, not to "download", neither to "storage scopes".
Signal can't see in the Standard Notes directory
If I set the rights for signal above, to download, then yes, it will be able to see all the other directories.