Function to reverse the order in the WP srcset array

WP-reverse_srcset_order.php

function reverse_srcset_order($atts) {
  if (isset($atts['srcset'])) {
    $srcset = explode(', ', $atts['srcset']);
    $srcset_reversed = array_reverse($srcset);
    $atts['srcset'] = join(', ', $srcset_reversed);
  }
  return $atts;
}
add_filter('wp_get_attachment_image_attributes','reverse_srcset_order',1,1);