I agree with everyone that exact figures cannot be arrived at, if only because people will disagree on which types of deaths to include.
For instance, "Does this count the 2 million Soviet POWs the Nazis murdered from 1941-42?"
Depends what you're counting.
BTW, Stalin killed some large but unknown number of Soviet POWs after their repatriation, perhaps close to this number. The official position of the Soviets during and after the war was that every single Soviet POW was actually a deserter and under a sentence of death.
Oddly enough, a great many of them in the early days of the war probably were more or less deserters. After 24 years under socialism they couldn't believe that the Germans could be worse.
Didn't take them long to find out they were indeed worse, for Slavs at least, but by that time many had already been captured.
Depends. I once worked for a Ukrainian fellow (who nevertheless was as Slav as they come) who deserted the Soviet army in '41 and actually fought for the Nazis for 4 years, mostly in anti-partisan units. The war stories he told were some of the most unspeakable things I have ever heard. Forty years later, he had zero ill will toward the Germans, but he still hated Soviet communism like gangrene.