Show thumbnails in feeds using the RSS widget block

I’m working on a new site and pulling in some content from my other sites via RSS. I’ve configured the sites with the originating feeds to add a thumbnail to the feed by adding a filter to the child theme functions.php file. However I’d like to get the RSS widget block on my new site to display those thumbnails when it pulls the feed items, and to change the link target to open links in a new tab. Is there a way I can do this with a hook or filter that doesn’t involve using a different RSS aggregator plugin? An example feed can be found at theblindmansworkshop.com/category/projects/feed. Any help greatly appreciated!