The trick is to create 1 popup, called “Popup” for example. This popup you set on display:none by default, to hide it when the site opens. Then create an interaction on a link which you call “open popup”, to open the popup. Then create another interaction to close the popup, obviously.
Now, if you have multiple popups. You might want to move this popup element inside another div-block element called “popup wrapper” for example. That way we can set the “open popup” element to "affect element “POPUP” and check the setting “Limit to sibling elements”. That way it won’t intervene with the other popups in your page.
See images:
