In the webinar camera and mircophone are automatically switched off. If the lecturer allows it, both or only one of them can be switched on in the lower left corner of the window by checking the respective checkbox. In the audio settings you can also individually set a check mark, but the microphone and camera should be switched off when joining the meeting. Please also note that the view will be displayed differently if you use "Zoom" with your mobile phone.
By the way, camera and microphone can only be accessed if you allow it. In a webinar you can only speak if the lecturer allows it and you are explicitly enabled to do so. Information on data protection when using Zoom can be found on this website.