Facebook sometimes sends me a second notification for events, in particular when I haven't pushed "Attend" nor "Decline":
How to disable these "Don't forget" notifications?
I still want to receive the first notification (when I get invited) but not the subsequent "Don't forget" notifications.
Note: I receive too many event invitations to decline them all individually.
Enter those events and delete the invitation. It will be as if you were never invited in the first place, thus no reminders.
Alternatively, block "problematic" friends from ever inviting you: https://www.facebook.com/help/211763458854062
Now, in both solutions the relevant parties won't be notified about what you did. But obviously they can tell the relevant events are not in your event list and that you're not in the guest list. If that's a problem, just turn off the relevant events’ notifications: https://www.facebook.com/help/356258654474400
