If you are okay with adding some code to your site to accomplish this, it’s pretty easy to do. You can add this to your theme’s functions.php file or wherever you keep code snippets. Please practice safe coding, back up your files, etc.
The filter you want to use manages the list of image sizes:
add_filter( 'send_images_rss_thumbnail_size_list', 'prefix_add_image_sizes_to_rss' );
/**
* Add new registered image sizes to Send Images to RSS options.
* @param $sizes
*
* @return array
*/
function prefix_add_image_sizes_to_rss( $sizes ) {
$sizes[] = 'shop_thumbnail';
$sizes[] = 'shop_catalog';
$sizes[] = 'shop_single';
return $sizes;
}
Those are the names of the WooCommerce image sizes–you can use all of them, or comment out/remove the lines for the sizes you do not need. HTH
