Two things: Many international law scholars hold that permanent security council members have a duty to act, including unilateral intervention, if a determination of genocide is made. That is why the declaration and word used matters deeply.
Second: It’s well known that the Red Army indiscriminately murdered and raped its way through occupied lands, collaborator states, and Germany itself. This is almost wholly an academic subject and bringing it up publicly in the affected nations is taboo, especially Germany. They’ve been given a complete pass because they were fighting real Nazis. Russia has done zero soul searching, even to the admittedly low official level we have done with regards to indiscriminate bombing raids or the atomic bomb.
When Russia announced a campaign against Nazis, this was the intended and entirely predictable result.