According to the Jewish Virtual Library, [0] the “5 million non-Jews” figure was invented by Simon Wiesenthal. He intentionally concocted it by subtracting 1 million from the estimated number of Jewish victims.
According to Wikipedia, [1] at least 8.5 million non-Jewish Soviet citizens were massacred by the Nazis (both civilians and POWs), and also at least 1.8 million Poles. The victims among the groups you explicitly mentioned, by contrast, added all together number no more than 1 million. It is controversial, however, whether the term “Holocaust” should be used for all Nazi genocides and atrocities, or restricted to only include the Nazi genocide against the Jewish people.
[0] https://www.jewishvirtuallibrary.org/non-jewish-victims-of-t...
[1] https://en.m.wikipedia.org/wiki/Holocaust_victims