Unfortunately, only Google Drive allows sharing of diagrams with other users (including real-time collaboration between users). We strongly recommend to use Google Drive to store your diagrams where possible.
You can share draw.io files with other Google Drive users in the Google Drive interface.
Google Drive also allows the option to share within the application itself, using the blue "share" button top right in the app.
If you are not using a cloud storage option and are saving the diagrams locally, you must manage your diagrams yourself, we do not have copies of the diagrams and cannot offer sharing functionality.