David Baumwald

After WordPress 5.7 is released, iframes will have the <code>loading="lazy"</code> attribute added by default. See Trac ticket <a href="https://core.trac.wordpress.org/ticket/50756" rel="nofollow ugc">50756</a>, and changeset <a href="https://core.trac.wordpress.org/changeset/49808" rel="nofollow ugc">49808</a> for the actual implementations in core.
This plugin, for the short term, is a global disabling of lazy loading for all iframes, no matter their context.
Changelog
<h4>0.1.0</h4>
<ul>
<li>Initial pre-release.</li>
</ul>

Disable Lazy Loading for IFRAMES

A small plugin to quickly disable the lazy loading for iframes in WordPress 5.7 and beyond.

Logan Graham

A simple plugin to enable lazy loading for all images using WordPress image functions, or embedded into posts and pages using the WordPress dashboard.
The plugin works by replacing the original image source with a blank transparent gif via datauri. Reducing page load speed, network requests, and saving bandwidth for host and visitors unless they scroll where an image is in view. The plugin makes use of the fantastic <a href="https://github.com/aFarkas/lazysizes" rel="nofollow ugc">lazysizes</a> javascript library.

WP Lazy Loaded Images

A simple plugin to enable lazy loading for all images using WordPress image functions.

Disable Lazy Loading for IFRAMES vs WP Lazy Loaded Images