"Darwinism" in modern use is almost only used by creationists, instead of the correct term "evolution".
It's absolutely true that Darwin was a racist, though for his era and background he was relatively "woke". See https://freethoughtblogs.com/pharyngula/2007/03/22/was-darwi... for an example of an anti-creationist listing some of the ways that we can judge his level of racism.
(Note specifically 'Darwin noted the inherent injustice of slavery. Darwin argued it was racist and unjust, and therefore unholy. FitzRoy loudly argued slavery was justified, and racism was justified, by the scriptures.' Can Christianity ever separate itself from racism? But that would be both-sideism.)
Asserting that evolution requires saying that some are "subhuman" is emphatically not true. It's not hard to demonstrate. The example given is that 'Homo erectus pekinensis' is called "subhuman".
A quick check in Google Scholar shows that, yes, indeed, papers up to the mid-20th century used that term in combination with Homo erectus pekinensis. However, of the 1000+ publications containing "Homo erectus pekinensis" only a handful also contain "subhuman", and the ones I could read were always quoting the older literature.
If it were "impossible to separate", why does it appear to have separated?
> The word “creationism” is used unfairly as a cudgel against proponents of intelligent design.
As a reminder, this association was also affirmed by the US court system in Kitzmiller v. Dover Area School District. Among other things, it was demonstrated that the intelligent design textbook "Of Pandas and People" was written by taking a creationist textbook and replacing "creationism" with "intelligent design", "creationist" with "intelligent design proponent", etc.
It's therefore more correct to say the term is being used fairly as a cudgel.
Or, that "Darwinism" is used unfairly as a cudgel for modern evolution.
So, as the other commentator says, evolution implies some races are "more favored" than others, i.e. superior. Outside the modern negative connotations of "racism" Darwin's title is racism in a nutshell: the claim that some races are superior to others. In turn, this doesn't mean that the "superior" races need to exploit the "inferior" races, that's an added assumption. The "superiors" could instead use their power to benefit everyone else.
This is in contrast to the common religious view point that even though some people may have more talents than others, this does not make anyone inherently superior to another in that they are more valuable and more worthy of preservation.
So, Nazis can endorse their brand of human driven evolution quite consistently with Darwin's view. However, Nazis have to twist religious doctrine to support their view.
Evolution requires that some races are more suited to specific environments than others. It says nothing about absolute superiority.