Novalissoide LOL, I tried Denying access to "Music and Audio" and saw:
"Access to photos and videos also won't be allowed. This app doesn't support the latest version of Android. If this app can't access music and audio files, it also won't be allowed to access photos and videos"
:)
i went Back, turned on Storage Scopes on "Music and Audio", left only the folders I have the pictures/videos I want handled in.
NOW it looks really weird -- in the Allowed section I have scoped "Photos and videos", "Files" is shown of the list of not allowed, but when I tap it it shows "Allowed" is selected.
"Music and Audio" also shows in not allowed list, but when opened for details it shows "Don't allow (+Storage scopes)".
Results seem to be exactly as desired (so pictures+movies from the selected folders only, no infinite spam from every single folder possible), it even respects .nomedia as expected.
So weird.
Thanks for the workaround idea; I'll report back if something is seriously broken (maybe some internals use the Gallery for file picking or something).