Toussaint As you have noted, login and permissions in Files Gallery is very basic. There is only one login, and permissions for various file manager commands are either on or off. Soon, there will be a new version where you can assign multiple logins with different permissions per user.
However, I don't necessarily have specific plans to allow different permissions on a per-folder basis. This requires an extremely complex configuration, where you must assign permissions, for each action, for each user, for all the different folders. This is something like filerun.com and nextcloud.com might be capable of, but these are heavy multi-file applications that require database.
Why not create a public version and a login-version that points to the dirs that you want to be able to edit? This could even be achieved by creating symlinks to the editable dirs from the admin-version.
I may consider this in a future release, but per-folder per-user per-action based permissions isn't something on the immediate radar. This might only be possible by storing a file
_files.json in each folder, that contains the configuration for each user for what they are allowed to do in the folder.