As others have said, this is a matter of definition. There are many older claims of such mass exterminations, but without the modern day efficiency of a Heydrich, it was hard to be as thorough as people would have liked, especially if you allow for intermarriage.
This is a particularly sensitive issue in Australia, as you would well imagine. The last full blooded Tasmanian Aboriginal died in 1876. But there are a lot of people of part-Aboriginal descent in Tasmania, who claim that heritage, and who do not want to be told that they don’t exist.
There are plenty of people on Quora who will tell you there is no such thing as race, biologically. I guess. But there is such a thing as race, culturally, and there is such a thing as culture. And there has certainly been no shortage of cultures exterminated from the face of the earth.