jmarreros

This Plugin allows to use an external image as Featured Image, this can be especially useful if you house your images in another location.
This Plugin is compatible with Nelio External Featured Image Metadata, so you can reuse your data in case you want to uninstall Nelio Plugin.

External URL Featured Image

It is what I was looking for: simplicity.

$external_image = get_post_meta( $post->ID, '_dcms_eufi_img', true );

Works well for me

Use an external url image as Featured Image for your posts, pages, and other kind of post types.

Archivarix

Archivarix External Images Importer will scan your posts and pages for external urls in src/srcset attribute for all img tags. Based on configured settings it can:
<ul>
<li>Download images from their external locations</li>
<li>Download images from Internet Archive (Wayback Machine)</li>
</ul>
You can choose what to do with images that could not be retrieved from external sources.
For further information and instructions please see <a href="https://archivarix.com/en/wordpress/" rel="nofollow ugc">Archivarix WP Plugin</a>

Archivarix External Images Importer

Works great!
I imported several posts into a site running WordPress 5.9.3 with Gutenberg and the Archivarix External Images Importer plugin imported the external images without any issues. I've tested a few other image importer plugins but none of them had the ability to scan a site and import from existing content like this one does.

Works with Gutenberg

Import external images in posts and pages from its original external sources or Web Archive if original source is unavailable.

External URL Featured Image vs Archivarix External Images Importer