Right? Funding media is one thing and using state/academic authority to alter history is a whole another level of crime. I borrowed the book from my sister to transcribe the chapter about USSR, I might share it as a curiosity later this week.

There are few fragments straight from the official history textbook for secondary school in Poland:

After Lenin's death and against his will, [Stalin] became General Secretary of the party. During his reign he eliminated all his political opponents and implemented in the country industrialization and collectivization. These measures, together with widespread terror policy caused millions victims in the USSR. In 1939 Stalin collaborated with Hitler's Germany, which resulted in assault on Poland and division of it's terrotiry.

(I bolded selected text by myself)

"Even so Stalin continuosly tried to rebuild close relations with [nazi] Germany, because both countries still had the same political interests. Soviet dictator was impressed by panache and efficiency of Nazi regime. Special impression supposedly made on him "Night of the Long Knives", when Hitler murdered his opposition inside the party [...]. Even during bitter competition, both totalitarian powers tried to create a common border, but main obstacle was existence of independent Poland.

Later on they write that both countries finally got to an agreement and launched a common assault on Poland, but Hitler supposedly betrayed Stalin and the alliance ended in 1941.

I guess when USSR and Reich supported opposite sides during Spanish civil war it was a clear sign of friendship or something.

YO! I know exactly what you tare talking about. I saw that same shit at some point (I think around the time it first aired), and it had honestly painted my understanding of the start of WWII badly. Especially because back then I didn't care about learning anything about the Soviet front as they were also always spoken about as being basically the same as the Nazis. WWII is always about the US "saving the day" when talking just about the war and not the genocide elements. I even have cringe memories of parroting the "Stalin and Hitler were best buds, and that Stalin basically only ever really trusted Hitler which fucked him up when Hitler turned on him" shit. Though it is personal cringe as I never got any push back or ever corrected, thankfully I don't think I really focused on it enough to bring up with many people. I am just glad that even one other person remembered seeing that shit to verify it being a real line of "educational material."

Poland invaded the former Russian Empire during the russian civil war. It annexed large areas.

The USSR tried to revive the Entente for years, but was rebuffed by France, GB and the US. Partially because local fascists, partially because these nations had no real interest in a new entente, partially because Poland lobbied against the USSR.

Then the Munich conference happened. Previously the USSR was the only nation willing to military support Czechslovakia, but was denied military access by other countries to get there. Czechslovakia ceased to exist and was carved up by its neighbours.

This made it clear to the USSR that their dream of a new Entente had ended and the western capitalist nations wanted to direct germany eastwards against them. So they did two things:

1. Sign a non-agression-treaty with germany. As the last european state to do so. This lead Germany to move west first.
2. Offer Poland a defensive treaty. Poland denied, because of anti-soviet tendency and pro-german one.

So when Germany invaded Poland, the USSR did fuck all for two weeks. Then, after the polish government had left for exile, they moved to the territories Poland had annexed previously and occupied them. The Polish governments last order before exile were not to resist the Red Army.