Using older versions of Outlook for Mac for personal email and calendar
The agent didn't work but follow the 'On MacOS Ventura: Remove Microsoft Exchange Account and Re-add' in the following link. I did this with multiple accounts and tested new meetings on iMac, which then showed up on other devices and vice versa.
https://www.howtoisolve.com/exchange-calendar-not-syncing-in-macos/
It works for now ... let's see how long that carries on for. Maybe it was a bug with the switch to VenturaOS - but I just know it works now. It shouldn't happen, though!!! Good luck everyone.