How do I create a pop-up ONLY for my mobile site, not my desktop?

https://samanthagalvao.com

I want to add a disclaimer popup to my website only in the mobile formate. I'd specifically like to add this popup only to the mobile site to encourage viewers to move to a desktop view — since this is a portfolio site, it's often encouraged to direct employers/viewers to a full view of the creative work so everything can be evaluated properly. 

Is it possible to create a pop-up ONLY for my mobile site and not my desktop?

You can enable Promotional Popup then we can give the code to disable it on desktop