Germany creates the Mitteleuropäisch Räterepublik (Greater Germany merged with Brest-Litovsk satellite nations in Eastern Europe alongside the post-Austria-Hungary states) that just so happens to engage in Holodomor-style targetted famines against "nationalists", in particlar the Poles? And these anti-nationalist campaigns along with anti-religious campaigns target the Jews due to Zionism being a banned ideology. Dissidents against the regime are sent to labour camps to perform forced labour under brutal conditions until their release--or more likely, death.
Maybe a lot of this happens during a World War II analogue brought on by the Mitteleuropäisch Räterepublik's series of annexations, in which case as the war turns worse (maybe against the USSR, once an ally now turned enemy in some great schism in global communism) they become increasingly desperate for labour and increasingly paranoid about enemies. Here I could see things like the "stab in the back" legend take a prominent place where the "Zionists" are blamed for why Germany lost not only the Great War, but this war too. Like in the Soviet Union, Jews would be targetted because perhaps some purged communists in the Mitteleuropäisch Räterepublik were ethnic Jews and the belief the USSR is ran by Jews who perverted true communism. Some analogue to the Doctors' Plot would occur except in Mitteleuropa, would actually be carried out in full, and the Jews would all be sent to labour camps. For "efficiency", prisons who become too weak to work in the declining conditions are exterminated at newly built death camps. Hostile nationalities like the Poles are similarly deported to the ever increasing number of labour camps, and closer toward the frontlines in France and Belgium, entire towns (mostly of French speakers) are massacred or deported to the camps. Many perish in these camps of disease and starvation.
It's difficult to make a monstrous Red Germany without it just being another take on Stalinism in terms of atrocities, although this take on German communism would be fused with Prussian militarism in the same manner Stalinism inherited many traits of Tsarism. I think either of the Strasser brothers, TTL turned communist, would make good "German Stalins" (or otherwise wind up as German version of Trotsky or Bukharin).