Hi @Jeffrey ,
Can we confirm if your iCloud email account is set up as iCloud or IMAP on the new Outlook?
For the Classic Outlook or Old Outlook, you may install app for iCloud Set up for automatic syncing - Set up iCloud Mail, Contacts, and Calendar in Outlook on your Windows computer - Apple Support. In the new outlook, you can setup an iCloud account directly in the client.
Please check your iCloud account configuration via: Add or manage an iCloud email account in Outlook
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