You're so caught up on "the cold winter theory". I'm telling you that you can completely let it go. It's one (pretty good) theory to explain one selection pressure that may have contributed to some of the aggregate divergence we see across races.
Even if you started with two seperate genetically-identical groups in identical environments, over enough generations you would expect at least some variation to emerge due to random chance (accidental deaths, mate selection, DNA recombination, cultural practices, etc). That is the point I would like you to take away from this exchange.
How would you explain how geographically distant groups in radically different conditions could, over millennia, converge on all of the exact same non-visible traits without even minor variations? I truly can't imagine a way that this would be possible aside from the infinitesimally unlikely product of completely random chance.
The premise was more that we can say with near-certainty that there are non-visible genetic differences between the races without even knowing specifically what these traits are or the extent to which they have diverged. We know this based on our understanding of genetics, natural selection, migration patterns, randomness, and the passage of time.
It would actually be quite the story if the races were somehow identical in all of these traits.
Both of these positions are untestable. One, however, is extremely likely while the other would be a miracle even in the wildest fantasies of the wokest progressive.