Insufficient Privileges Salesforce Error When Deleting an Event from a Public Calendar

Events on a Public Calendar cannot be deleted by a user unless one of the following conditions is met: the user is the owner of the associated parent record, the user has the "Modify All Data" permission on their profile, or the user has "Modify All Records" on the associated or related object. This behavior occurs because the Activity object's Organization-Wide Default (OWD) sharing setting is set to "Controlled by Parent," meaning the parent record controls delete access for the Event.
The following workarounds are available:

Workaround 1: Set the Activity Object OWD to Private

Change the Activity object's Organization-Wide Sharing Setting from "Controlled by Parent" to "Private." With this setting, a user can delete any Event from a Public Calendar as long as the user has "Full Access" permission assigned for that Public Calendar and has "Edit Tasks and Events" enabled on their profile. The Event record is no longer controlled by the associated parent object.

Workaround 2: Remove the Related Object Association from the Event

Edit the Event record and remove the Related or Associated Object name from the Event's related field, then delete the Event record. By removing the parent object association, the Event is no longer controlled by the parent's sharing rules.