The settings are defined within your Zoom account.

You may want to have chat visible to all until your pitch (cta) and turned off after that.

You may want your attendees to be able to send messages to you, the host, or to panelists or even other attendees.

Or whatever the case may be.

To see the full tutorial on how to change these settings, please click the links below:

Chat Enable/Disable
https://support.zoom.us/hc/en-us/articles/7606407669773

Zoom Webinar:

https://support.zoom.us/hc/en-us/articles/205761999-Chatting-in-a-Zoom-webinar

Zoom Meeting:

https://support.zoom.us/hc/en-us/articles/203650445-Chatting-in-a-Zoom-meeting