Can I disable the magnifying glass and keep only the lightbox effect?

Unfortunately, it's not possible to disable the loupe function and keep only the Lightbox effect. The lightbox effect is just an optional feature that comes with the app, ultimately the app's main purpose is to magnify the product images with the loupe. So, it's not possible to keep only the Lightbox effect.

Alternatively, if you would like to keep only the lightbox effect, you might want to take a look at our Full Page Zoom app. This app doesn't have a magnifying glass, and you'll still be able to display your product images full-screen size. You can see it in action at our demo store https://stunning-landscapes.myshopify.com/products/surf-gallery, and you can test the app free of charge for 30 days.