Do you have the Apple TV box? If so, which model? Identify your Apple TV model - Apple Support. It is the Apple TV box that has Conference Room Display mode with the floating instruction message.
If this is about a TV that is AirPlay-enabled, then any message relating to AirPlay may look very different, and would have nothing to do with Conference Room Display AFAIK. Verify your AirPlay settings on the Vizio (see TV manual). Turn it off if you are not using it. Set access control rules to block unwanted AirPlay from nearby devices. Add the TV to the Home app on iPhone/iPad/Mac, and assign it a room, for use with HomeKit and AirPlay 2.