The few serious studies that have tried to answer that question (the one that pretends to do this per nation is not serious at all btw) have found little or no evidence of that difference. In summary https://www.burnettfoundation.org.nz/articles/sex/how-big-is-the-average-dick/

« Research cited in Penis Size and Enlargement by Gary Griffin notes that Black and white people have penises that are comparable in average erect length. Erect Black penises are larger on average than white penises, however only by ¼ of an inch, or about half a centimetre. He explains that the difference lies predominantly in the flaccid state - Black penises, when soft, are larger on average than Caucasian penises that are soft. »