A Modal or Lightbox image is an image which will show up if a user click on Magnifying-Glass icon on the upper-right corner of product's image.
This feature is enabled by default in Jupiter X, but you can disable it if you want.
In order to Enable/Disable the Image Lightbox for the single product image in Jupiter X:
1. From WordPress left menu go to Jupiter X > Customize.
2. In Customizer, click on Shop > Product Page
3. Enable/Disable the Image Lightbox option.
4. Publish the changes.