Starting September 27, 2020, Zoom is requiring all meetings (new and old) to either have a Passcode or Waiting Room enabled to ensure safer, more secure meetings. Zoom will enable a Waiting Room for your meetings if neither is enabled. If you already have a Passcode or Waiting Room on, there will be no change to how you schedule meetings. If you add Passcodes to an existing meeting/recurring meeting, calendar invites will need to be re-sent to include the Passcode, whereas new meetings that have Passcodes enabled will have the Passcode included in the meeting invite automatically. If Waiting Rooms are enabled, there is no change to how you schedule meetings.
If you are wondering why Zoom has decided to make this change, please visit this link to Zoom's FAQ article:
https://support.zoom.us/hc/en-us/articles/360045009111-FAQ-Meetings-Waiting-Room-and-Passcode-Requirements-July-2020
This article also shows how to see which of your meetings have Waiting Rooms or Passcodes enabled.
The following links will help guide you on how to set up/use Waiting Rooms and Passcodes on your meetings:
Enabling/Using Waiting Rooms
Please click the following link for the step-by-step guide on Zoom Waiting Rooms.
https://support.zoom.us/hc/en-us/articles/115000332726-Waiting-Room
Adding a Passcode to Your Zoom Meeting
Please click the following link for the step-by-step guide on Zoom Meeting Passcodes.
https://support.zoom.us/hc/en-us/articles/360033559832-Meeting-and-webinar-passwords