Facebook Events (calendar items) exist in some sort of Facebook twilight zone. Neither completely abandoned, nor entirely useful. You can, for example, subscribe to an Event stream in Google Calendar. That’s a useful move.
Even public events are rather hard to share however. Facebook’s limited (usually obsolete) official documentation suggests copy and paste the URL. As of today this also works...
- View Event and choose Join.
- Look for the (mislabeled) Invite drop down - select it.
- Choose Share Event.