Hello.
It looks like part of this has been answered already: [Help] How to hide photos from the photos app
However, the .nomedia flag is an overloaded file that is also used by the preview generator app to exclude generating preview thumbnails for files in that folder and any folder further down.
Is it possible to do something like .nophotos to exclude files from a folder but still allow preview generation when browsing through the photos in the files app? The on-demand preview generation puts a significant load on the server so it would be nice to have the best of both worlds.