The following code is added to the corresponding skin file of the widget. This will of course be overwritten in case of updates.
<article <?php post_class( $classes ); ?>> <a class="elementor-post__thumbnail__link" href="<?php echo esc_url($featured_img_url); ?> "> <?php
is replaced with
<article <?php post_class( $classes ); ?>> <a class="elementor-post__thumbnail__link" href="<?php echo get_the_post_thumbnail_url(get_the_ID(),'full'); ?> "> <?php