To restore this interoperability between the Webex Mac Outlook plugin and Windows Outlook plugin, you must upgrade your Webex The controls still showing Add Webex Meeting when users open an appointment and try to edit it. The Webex Mac Outlook plugin doesn’t recognize Webex meetings in Mac Outlook 16.23 or later for Microsoft Office 365, with Mac Outlook Plugin in the Cisco Webex Desktop App Requires Upgrade to Version 39.5.1
See the Webex Meetings Web App Known Issues and Limitations for info on the web app.