Each School site needs to opt into a public menu. You can do this by going the "School Menus" tab, clicking the drop down on the upper left hand side and selecting "Manage Menus"
There you can opt locations to be visible on the public menu portal
After clicking "Save & Close" go to the three dots on the top right side and click, "template editor" here you can customize the look and feel of your public menu.
From there you can go back to the three dot menu, and navigate to the portal or copy the public portal link.
Troubleshooting: If you are having issues with your public menu, please determine if
The school menu has been published
That the menu setting has been switched to "Visible in Public Menu"
That if it is a cycle menu, the cycle has an end date