In Chrome 76, you can use the loading attribute to completely defer the loading of offscreen images and iframes that can be reached by scrolling:
Here are the supported values for the loading attribute:
> auto: Default lazy-loading behavior of the browser, which is the same as not including the attribute.
> lazy: Defer loading of the resource until it reaches a calculated distance from the viewport.
> eager: Load the resource immediately, regardless of where it's located on the page.
Morten in https://core.trac.wordpress.org/ticket/44427 makes a good case for this. Can we work on this since it does not make any breaking changes? It is an enhancement that I see since I come from a location where we have bad bandwidth and network.
From what I could tell in the support forums, the original lazy load worked, but the attribute was added to all images. They fixed it so it wasn’t added to the header image.
In a later release, they added it to iframes. This caused problems, and I’m not sure that is all fixed.
I would put it only on images.