Even if someone has something like a specific immune system genetic profile that makes them more susceptible to a particular virus than other people, that genet

Even if someone has something like a specific immune system genetic profile that makes them more susceptible to a particular virus than other people, that genetic marker is extremely unlikely to correlate at all closely with any socially defined racial or ethnic group. The effects of European diseases on native American populations is a red herring in this context, as modern populations are increasingly interbred and not isolated, and even with that case, it's not entirely clear that it was genetic vs. developmental, i.e. European children who survived to adulthood likely had been exposed to those diseases when young, while native American adults had not - so if they had been exposed as children, there could have been no difference in susceptibilty.