I reverted back to legacy outlook and now my contacts and calendar are blank

Dear @Brian Johnson,

Welcome to Microsoft Q&A Forum!

Based on your description, I found in this article that accounts added in the new Outlook for Mac will not automatically be added to Legacy Outlook, and vice versa. So, may I know that you have tried to re-add your Outlook account in Legacy Outlook? If not, please kindly try to re-add it in Legacy Outlook. It may be related that when switching between the New and Legacy versions of Outlook for Mac, accounts do not carry over automatically, which is why contacts and calendar data may appear missing unless the accounts are manually re-added.

Reference: https://support.microsoft.com/en-us/office/outlook-for-mac-6283be54-e74d-434e-babb-b70cefc77439

Before you re-add account, please see this case that was partially similar to your case and it may be a small tip with it: https://learn.microsoft.com/en-us/answers/questions/5496670/how-do-i-see-all-email-history-from-legacy-outlook

You can consult in this link for re-add account in Legacy Outlook: https://support.microsoft.com/en-us/office/add-an-email-account-to-outlook-for-mac-6aeec61b-86af-40af-8ffe-985d0fc82ddb

I hope this information can help you.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment". 

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.