As a Wix Website Designer, clients often request popups on their Wix websites.
I always advise to use popups sparingly, as Google does penalize sites now for having overly obtrusive popups (like newsletter signups) that block the user from seeing the content. Sometimes, though, popups do come in handy for events or other temporary promotions.
Here are my quick tips on how to edit Lightboxes in Wix in the video above.
Also, not shown in the video – make sure to go into your Mobile View editor and edit the lightbox there as well to automatically show up, I believe by default the mobile lightboxes are NOT automatically set to popup so you need to turn that on if desired.
I like to use popups instead that respond to a button, so you can put a small button/blurb and link to a popup for more info, this way it's a little less obtrusive and also can load faster. Popups tend to have a delay that varies depending on the loading time of your page and what settings you setup for the delay.