Shared Outlook Calendar disappeared

An Outlook Calendar that my wife and I share has suddenly disappeared from my Outlook Calendar. It still shows on my wife's computer.

We set this up a number of years ago, so I have no idea where or how to troubleshoot this. I do recall that we had to each create outlook.com email addresses so that we could access Microsoft Exchange.

We are using the Classic version of Outlook. In case it's useful, here's the exact information from the Outlook About page: "Microsoft® Outlook® for Microsoft 365 MSO (Version 2605 Build 16.0.20026.20168) 64-bit."

Thanks to anyone who can help me solve this problem.