RCA File Desk has no site frontend. Visitors never see elFinder. All UI runs in administrator under Components, RCA File Desk.
Exposing a filesystem browser on the site front would be a security project of its own. RCA ships admin-only scope on purpose. If you need front-end downloads, use Joomla media fields, document libraries, or commerce download products instead.
The connector responds on an administrator index.php task with format=raw. That URL is not meant for embedding in articles or menus. Block or ignore front-end attempts to hit administrator routes.