Cannot view or edit an Event from a shared Calendar

There are three key conditions to be aware of when it comes to Salesforce Calendar Sharing.

Condition 1: Calendar Sharing Affects Visibility, Not Event Detail Access

Calendar sharing settings affect the visibility of items on a Calendar, but do not give access to Event detail pages. For more information, see:

• Share Your Calendar in Salesforce Classic
• Share Your Calendar in Lightning Experience

Condition 2: Required Permissions to View, Add, and Edit Events on a Shared Calendar

You can only view, add, and edit Events on a shared Calendar when both of the following are true:

• You have the "Edit Tasks" and "Edit Events" profile permissions to create and edit activities.
• You have access to the user's calendar.

Additionally, to be able to edit an event when the Default Sharing Settings for Activity is set to Controlled by Parent, the user must also have edit access to the Parent (related) record. See the "Activity Access" section of the Guidelines for Tracking Activities documentation for more details.

Condition 3: Events Without a 'Related To' or 'Name' Field Are Always Private

The 'Related To' and/or 'Name' field must be completed, or the Activity will be considered private regardless of other sharing settings (such as Calendar sharing).
For example, even if a user shares their Calendar with 'Full Access,' all Events that are not associated to another record will be private.
Note: If users receive the error 'Only event organizers can update this field' when editing an Event, it means they are attempting to edit a child Event record. Updates to an Event must be done through the parent Event record, which is located on the Calendar of the Event organizer.
If you are unable to view full details of an event from a shared calendar, please review: Unable to see full details of Events from shared calendar in Lightning.

Calendar Visibility for User-created Calendars

When a user creates a Calendar view from an object, only that user can see the Calendar. Previously, anyone above the user in the hierarchy, or anyone with the 'View All Data' permission, could see and delete the Calendar. This extensive visibility could cause slow response times.