Currently the sharing options for Webes, Zoom and MS Teams are through HDMI cable and share.webex.com, however there is a limitation for Google Meet sessions, where the only way to share is to access the generated URL from the session. It will be much convenient to have the HDMI and share.webex.com sharing option available for Google Meets as well.
The limitation is currently described under the following article: https://help.webex.com/en-us/article/nxx11sk/Join-Google-Meet-meetings-on-Your-Webex-Device#Cisco_Reference.dita_3b63e599-1d11-4227-a5aa-73398bd1dfff
Sharing over the device is not possible. You can do it by tapping sharing options and enter the provided URL in your browser.