Slavs are about 300 million, this would be impossible.
Yes, Slavs are
about 300 million now
, what does it have to do with the topic? Numbers of population grew rapidly after the 40s all over the world.
I think you completely missed the point.
Read again about the Nazi (National Socialism) concept of Lebensraum
and how it affected Poland. It was "Drive towards the East" - mostly to the Polish territories, that were adjacent to the lands populated by Germans - and were to be inhabited by the German settlers (Volksgruppen) from the Baltic countries, Lithuania/Belarus and former Galicia (Ukraine and Romania), like in this German map:
South Slavs and Russia have nothing to do with that, so there's no point in reminding basic facts everyone knows.
I'd advise you also to read about Poles that were exterminated in Auschwitz: auschwitz.org/en/history/