Hi Patrick,
Thank you for posting your query in our community.
Based on your description, when you try to insert Microsoft Outlook Date Control in Excel worksheet, an error "Cannot insert object" will occur.
From this official article: OlkDateControl object (Outlook), we can know that we can only add this control to a form region in an Outlook form using the forms designer; you cannot add this control to a Visual Basic UserForm object in the Visual Basic Editor.
Best regards,
Jazlyn