EndNote libraries are made up of two parts: the .enl file and the .data folder. These two parts must be kept together. Both are needed for the library to work correctly.
EndNote libraries should be kept on your computer's hard drive. Storing and editing libraries on a network drive can lead to corruption and performance issues. Don't keep in Teams or OneSource.
Don't store the EndNote library in cloud-syncing services such as DropBox, OneDrive, Box, SugarSync, etc. Over time your libraries can be corrupted. If you briefly store a library in a cloud service, it is vital to download before opening, and to have other back up methods.
Uninstall your previous version of EndNote before installing a new version.
Adapted from Clarivate's EndNote LibGuide