Salesforce Event Records Not Appearing in the Activity Timeline Due to Child Event Behavior

For Event records, a "parent event" record for the organizer and "child event" records for the attendees are created.
Only the "parent event" is displayed in the Activity Timeline; "child events" do not appear on the timeline.

When users are added to the [Attendees] field of an Event record, the system generates both the organizer's event (parent record) and each attendee's event (child record).
In this process, the [Is Child Event] checkbox is selected on the "child event" side. 
Verify this field using a report.

To edit or verify the details of an Event record, please modify the "parent event" record from the organizer's calendar or the record associated with the organizer.
Changes made to the parent record are automatically reflected in the child records as well.