Thanks for the input. After digging deeper into the Bricks dynamic data documentation and testing multiple approaches, I could not find a truly native way to get the featured image filename via Dynamic Data.
In the end, the only reliable solution I managed to get working was a shortcode that reads the attachment file directly from WordPress:
add_shortcode('featured_image_filename', function () {
$post_id = get_queried_object_id();
if (!$post_id) {
return '';
}
$thumb_id = get_post_thumbnail_id($post_id);
if (!$thumb_id) {
return '';
}
$file = get_attached_file($thumb_id);
if (!$file) {
return '';
}
return basename($file);
});
This works fine in Bricks, but honestly I do not consider it an especially elegant or Bricks-native solution, more of a workaround.
So if anyone knows a cleaner or more native approach using Bricks Dynamic Data or an officially supported API, I would be very happy to hear about it.