Dear @Stenson, Herbert H
Thank you for contacting Microsoft Q&A Support.
After checking your concern, I have tried to research in all material documents from any resources and I confirm that New Outlook still has limited support for third-party COM add-ins. More information, see: Feature comparison between new Outlook and classic Outlook - Microsoft Support
Therefore, if you really want to use Caldav in Outlook, I suggest you switch back to Classic Outlook which is available for COM add-ins and retry with the Caldav. Also, I would like to re-confirm that New Outlook is currently not supportive for COM add-ins third-party service including Caldav.
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