Hi @Timothy Davis ,
Welcome to our forum!
Currently, Outlook data file is not supported in the New Outlook. As a workaround, you can switch back to the classic Outlook at any time by clicking the toggle button in the top right corner of the window.
Someone has already submitted this feedback on the dedicated portal via the link below: https://feedbackportal.microsoft.com/feedback/idea/b53fae23-b5f8-ed11-a81c-000d3ae5b6f4
Many features of our current products are designed and upgraded based on customers’ feedback. With requirements like this increase, the problem may well be released in the future.
You can mark my reply as an answer, so that other users in the forum who have similar problems can also vote.
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