Sorry they are not night sights they are Black Co-Witness Iron Sights see *****Full-sized performance in a concealed carry package
Striker-fired autoloader
Double-action operation
Fully ambidextrous controls
FN Low Profile Optics Mounting System with plate adapters for direct mounting of more than 10 optics
******All-black co-witness iron sights https://fnamerica.com/products/pistols/fn-509-midsize-mrd/

These guys are all correct about black sights on the firearm you listed. I put info from 17 round capacity model 66913 with night sights---------budsgunshop.com/catalog/product_info.php/products_id/35826/fn+fns-9+4%22+black+17rd+night+sights

P John, the Sights are Co witness night sights. The SIGHTS are Black Co-Witness Iron Sights.

John, Yes this optics ready model has night sights. They are high enough to co witness with red dot optic when mounted.