How to use this module? Upload the library?

Sorry this is so frustrating. There doesn't really exist a simple solution for adding 3rd party library dependencies to Drupal modules. This module was basically forked from another deprecated module, Lightning Media, so I mostly just copied how things were done there.

In any case, this module has a dependency on the DropzoneJS module → . That module's page has information on how to to add the Dropzone JS library. It seems you did follow those instructions but are still having an issue. Can you try downloading version 5.7.2 of that library and seeing if it works? That's the version I use successfully.

I posted an issue at the DropzoneJS issue queue.
✨ Allow CDN to make the module work out of box Active

I think that using the CDN as a fallback would be the right solution for making it work out of the box.

Otherwise if we can't do that, then the only other option is to improve the documentation of this module and basically copy the install explanation from the DropzoneJS module.