Weston Ruter

This plugin adds the <code>loading=lazy</code> attribute to <code>iframe</code> elements coming from oEmbeds. In WordPress 5.5, <code>loading=lazy</code> is added to images per <a href="https://core.trac.wordpress.org/ticket/44427" rel="nofollow ugc">#44427</a>, and in 5.7 it is being added to iframes as well per <a href="https://core.trac.wordpress.org/ticket/50756" rel="nofollow ugc">#50756</a>.
This plugin will be obsolete by the time WordPress 5.7 is released. When that happens, this plugin will do nothing.

Lazy Loading oEmbed Iframes

Add the loading=lazy attribute to iframes coming from oEmbeds in content

edwardtownend

Requires the Advanced Custom Fields plugin. Output can be selected as HTML embed, URL, or data object. Includes settings for preview and output resolution and will accept any provider registered in WordPress.
With the news that ACF V5 includes a built-in oEmbed field type, we’re discontinuing further development of this plugin. The plugin will remain online for legacy V4 support to those that haven’t upgraded, but only essential updates will be released.
<h4>Compatibility</h4>
This add-on will work with:
<ul>
<li>Advanced Custom Fields version 4 and up</li>
<li>Repeater Field</li>
</ul>

Advanced Custom Fields: oEmbed Field

Adds an oEmbed field type to Advanced Custom Fields.

Lazy Loading oEmbed Iframes vs Advanced Custom Fields: oEmbed Field