You did a great job using credible sources, especially the U.S. Holocaust Memorial Museum, to show that Hitler played a major role in the Holocaust. I also liked that you brought in another reliable site to support the same conclusion. One thing that could make your factcheck even stronger is using Hitler’s own words from Mein Kampf or his speeches. He clearly expressed antisemitic views and goals, and quoting him directly would make it harder to deny his responsibility.
I would also suggest being careful when calling one source “less biased.” Both of your sources are trustworthy and based on strong historical research. Finally, you could add a quick response to the claim that Hitler “collaborated with other races.” That’s a big distortion, since his policies targeted many groups for persecution, including Jews, Roma, Slavs, and Black people. Addressing that would help round out your argument.