This is presently a gap that we are closing and expecting to deliver in approximately the May, 2021 timeframe. For now, to get the 'new meeting experience', please use the green toast/popups that you see in the new Webex App itself rather than launching from the calendar.
When we release the 41.5 update we will update the OS [Mac/windows] preferred app handler hook to launch the new meeting experience from the calendar as well.
Thank you!
~Joe Tansey