Check the folder synchronization for calendar.
The latest version (16.26 (19060901)) has issues when a new invite is received, it's not showing on the Outlook client. It shows online, though.
The issue happens when I send my computer to sleep and Outlook is disconnected from the network. I have to quit Outlook and open again to get the updated calendar entries.
The latest update to Outlook for Mac (16.26) seems to have broken synchronization of calendars across devices. If I accept an updated meeting invitation with new date/time within the iOS Outlook app, the change DOES NOT get reflected in the desktop application until I quit Outlook and re-open the application. This should NOT be considered acceptable.