Hi Mike,
Thanks for your reply. To troubleshoot this issue, please try the following steps:
1. Remove the current office 365 identify in your Mac via the steps in the article below:
https://support.office.com/client/Manage-identities-edc1a942-8242-46bd-8a9b-076553d5494d
2. Capture a screenshot of the login page and post back. To upload screenshots, you can click Use rich formatting in the forum and then click the icon of Insert Image.
3. If it is convenient for you, could you try to reinstall Office applications and check if there is any improvement?
Please let us know any update and we will provide further assistance.
Best regards,
Rachel Zhang