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" >