How to prevent downloads

Is there a way I can make users SEE the files in a folder, but can’t DOWNLOAD them?

What do you mean if your users should be allowed to SEE files, does it include viewing its content?
Because from my understanding viewing is also a kind of downloading. As far as I understand it is never possible to prevent a download, except you pipe a directory content to a viewable file.

You are right, it depends on the content. In my case, I just want to make users see the file list (they are audio files). But they will not be able to play/preview/download. Any ideas?

Due to the fact that you only want to provide a file list but not the files itself, it doesn’t matter via which path the users will get access to this information. You could e.g. pipe the result of the ls command to file which you provide to your users, like: ls -l > file-list.txt.