Eugenics; To generate "good" ("eu"), one should select for the most apt. Politically implemented eugenics came straight out of the idea of the "selection of the fittest" (Spencer, a Darwin associate, dixit). Selection of the fittest had supposedly given birth to the human species, according to Darwin, the way Nietzsche saw it... That explanation denied the will to power of the human species as a driver of evolution... Opting for cancellation instead. Nietzsche hated all that.
Nietzsche was not naive. He understood that "good" was dependent upon how it was defined by particular tribes or types, and he hated many of these definition of "good' which often embraced what he viewed as inferior, and, or, slave morality. In particular, gross, base, anti-Semitic, anti-French and anti-Slavs German commons... who had inverted all values, and were preparing monstrous wars.
The fanatical racists wanted to expel the Jews from Germany. Thus Nietzsche saw how "Darwin" was exploited, and counter-argued that the anti-Semites were obviously inferior, so should be expulsed instead of the Jews.
As Nietzsche predicted that mentality brought horrible wars. The Nazis used that "Darwinism" as the "scientific" basis that they were looking for to have an excuse to cancel others.
This being said, the best ideas on evolution attached to Nietzsche, Lamarck, and Darwin are still in place to suggest further advances in the theory of evolution. The force towards complexification of Lamarck is still a star guiding the will of many specialists of evolution. We even have now a mechanism in place: the (weak) hydrogen bonds of DNA modified by variegated quantum environment (in particular from the exertion of will).
In any case, even hard core Darwinists admit that the will of conscious subjects influence sexual selection, thus evolution. So Nietzsche won them over, in some sense.