Outlook for Windows Opens w/iCloud Calendar Erratically

Hello. A Windows 11 user was just added to our network... the only one. Awe added iCloud for Windows and sent an invite for a shared iCloud calendar. He accepted and the calendar shows in his web iCloud calendar account properly.

When he opens Outlook for Windows from the Windows Start menu the shared calendar isn't there.

If he opens the iCloud for Windows app and then opens the link to Outlook in the "Apps Using iCloud" screen a slightly different looking Outlook appears with the shared calendar.

Any idea what might be causing this and how to remedy it? Thanks.