Using older versions of Outlook for Mac for personal email and calendar
Dear Lou Bryant,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
According to your description, please kindly try to delete Outlook for Mac Keychain to check the result, for more details: delete any modern authentication tokens from the keychain
If your problem persists, since we specialize in technical support for Microsoft 365 Business Exchange Online, which is not professional for the Outlook for Mac, in order to better help you and no longer waste your more time. I recommend that you ask for help from our dedicated team, where technical engineers specialize in these related issues, and experts will focus on inquiries to further assist you, for details, please kindly refer to: Contact support within Outlook for Mac
Thanks in advance for your understanding! Your patience and cooperation will be highly appreciated. Hope you all the best!
Sincerely,
Kerry Chen | Microsoft Community Moderator