Save your complete library (the filename.enl file as well as its associated .Data folder and all of its contents) to a single compressed filename.enlx file in order to easily back up your library or send a copy to a colleague. Later, you can easily restore (unzip) the compressed library with EndNote.
To save to a compressed library file:
To restore a compressed library file:
NOTE: EndNote libraries larger than 4 gigabytes or 65,535 files cannot be compressed with EndNote’s Compressed Library command.
Information from: https://support.clarivate.com/Endnote/s/article/EndNote-Moving-backing-up-or-transferring-libraries-to-another-computer?language=en_US