Enabling Experience Cloud Sites in an organization adds a 'Public' field to the Activities object. This field allows users to make their Task or Event records available to Experience Cloud Site users above them in the hierarchy.
This field is hidden by default so Administrators will need to make it editable via field level security and visible on the Event page layout. Once it is available, the field must be checked to make the record available.
Alternatively, you may create a flow to update the public field as outlined in the article, Portal or Site Users do not see Activity history on their Accounts .
For example, when a company enables Experience Cloud Sites for the first time and a Partner Portal user tries to view an event owned by someone below them in the role hierarchy, they see 'Insufficient Privileges', even though the event's owner granted access."
The activity detail page should now be accessible to portal users above the event's owner in the hierarchy.
If user's continue to see an insufficient privileges message you may also check the following:
See also:
Cannot view or edit an Event from a shared calendar
Sharing Default Access Settings
Guidelines for Tracking Activities
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