Here are the steps you need to follow to disable the creation of public boards in your organization:

Step 1. Access your team's page, find the "My organizations" feature, and click on the 3 dots icon (ellipsis).

Final Step. Now click on "Disable public boards" to disable the creation of public boards in your organization.

Note: When this feature is enabled, no one inside your organization will be able to create new public boards (including the Owner of the Organization.)

You can enable the creation of public boards again at any time. To do that, follow the steps below:

Step 1. Access your team's page, find the "My organizations" feature, and click on the 3 dots icon (ellipsis).

Final Step. Now click on "Enable public boards" to enable the creation of public boards in your organization.