This is an accepted solution.
I haven't ever found an app to lazyload images in shopify.
Most themes have proper lazyloading, usually when you hire a developer to add a new section they might forget to add lazyloading.
The simplest way to enable lazyloading is to add loading="lazy" to your image tags.
like < img src="whatever" c lass="stuff" alt="a thing" loading=lazy" >
Hey, not sure if you still need this but it might come in handy for people with similar problems. We've recently released an app called Lazify that can automatically lazy load description images with one click.
You can check it out here: https://apps.shopify.com/lazify-lazy-load-images-1
Hope that helps!