Unscheduled Events on SharePoint Calendar
Take advantage of the Unscheduled Events Pane on the SharePoint List (Calendar View)
Microsoft Lists Calendar: Unscheduled Pane
You can view all the things that are still missing dates from the Calendar view by using the new feature, Microsoft Lists Calendar: Unscheduled Pane. The Unscheduled tab in the events pane to the right of the calendar view will display these things.
Unscheduled Pane in Microsoft Lists Calendar Views
Last year, Microsoft released the Calendar view feature for SharePoint Online and Microsoft lists for modern experience and later added support for using calendar views in List web parts on modern pages.
SharePoint: Microsoft Lists unscheduled items pane on calendar view
You can review all the items not yet appearing in the Calendar view due to missing dates. These items will appear on the Unscheduled tab within the events pane to the right of the Calendar view.
https://m365admin.handsontek.net/sharepoint-microsoft-lists-unscheduled-items-pane-on-calendar-view/