I would like to use the Ultimate Post List plugin instead of the default WP Category lists, but I cannot get the list to show up with thumbnail images. This note is to show what the problem is.
My movie reviews start with a thumbnail image of the movie poster. But I do not store the movie poster thumbnail in my WP Media Library. Instead, I insert a WP Block image with a URL link to an image on tmdb.org.
In a localhost test database, I activated the Ultimate Post List plugin and made a page with the list shortcode as follows. This example has all movies in the Romance category.