While sharing your screen/content, your Webex controls collapse into the orange button at the top of the screen. By opening the Participant Panel pop-up window, you retain the control to manage your Participants.
This only works when using the Desktop App on Windows or MacOS.
Hover your cursor over the orange button to open it.
Click on Participants to open the pop-up window.
Right-click anywhere in the pop-up to open the Participant context window.
Click on your desired operation.