William P. Davis

This plugin allows you to duplicate images you have in the media library and attach them to a new post, rather than having to create a new copy of the image and upload it to WordPress again.
It works by copying the post and its metadata. It does not actually copy the image. Any changes you make to the new copy of the attachment — updating the caption or cropping, for example, will only be applied to the new attachment, not to the original.
This is useful if you query posts for its attachments to display photos, or if you make use of galleries and have old images you might want to include, among other things.
To use, go to the Library tab in a post. You should see an ‘Attach’ link.

BDN Duplicate Images

Allows you to duplicate images in the media library and attach them to the current post.

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.

BDN Duplicate Images vs Archivarix External Images Importer