Hi @fiona92,
Thank you for reaching out to us. Sure, I will be happy to help you set a popup trigger via the navigation menu.
You can follow our step-by-step guide on creating your first Popup in Popups for Divi.
See here: https://divimode.com/knowledge-base/video-create-your-first-popup/
You can then add your popup ID to your navigation menu to trigger your popup.
See here: https://share.getcloudapp.com/Qwuw1DXE
Please note, when the popup is present on the current page, it will open; when the popup is not present, the menu item behaves like a normal menu item.
See here: https://share.getcloudapp.com/2NupZK8J
You can also refer to our knowledge base article “CSS Trigger” for further information.
See here: https://divimode.com/knowledge-base/how-to-trigger-an-area/#css-trigger
To trigger your popup on all pages via the navigation menu, you can use Divi Areas Pro.
See here: https://divimode.com/divi-areas-pro/
You can confirm the same in the demonstration video below.
See here: https://share.getcloudapp.com/p9uZmEy2
I hope this information helps. Please do not hesitate to ask any further questions. Thank you.