I'm going to focus on Episode 2: Lightning War.

I wouldn't say that both of these are 100% false, but they are inaccuracies that play into pretty standard tropes of the war that remove some of the nuance that I think is necessary in studying the conflict.

The episode details what it calls Blitzkrieg doctrine and it is the usual score. Tanks mass in their own formations, combine with air and artillery to strike at vulnerable points in a line, bypass strong points, and encircle formations on an operational level and not just a tactical one. While Operation Barbarossa in 1941 and later campaigns in the USSR certainly called for this, Blitzkrieg was more of a development of the older German "Bewegungskrieg" or "war of movement." Going back to the Prussians and Frederick the Great, the doctrine was to encircle enemies and do concentric attacks. The way popular media, including this documentary portrays the German Army makes it seem like the 1941 Wehrmacht was the 1939 Wehrmacht. Even in 1941, most of the Wehrmacht was powered by horse and not internal combustion. For Poland, Max Hastings gives the number at 400,000 horses and 200,000 overall vehicles in the invasion. Hastings even uses the word "blitzkrieg," and while the new type of fighting was formidable, I really believe it is important to stress that was a doctrine in development and would not reach its full capacity until later.

The second is the nature of Polish cavalry. While detailing the state of the Polish military situation, it shows clips of Polish Uhlans with lances, yes... but notice those rifles slung across their backs and grenades and other modern weapons? Everyone loves the lances and the legend is the legend. This documentary certainly isn’t the only one. Heinz Guderian in his memoirs mentions it and claims that the Polish cavalry had "in ignorance of the nature of our tanks, [the Poles] had charged them with swords and lances and suffered tremendous losses." The same Poles who had the 7TP and multiple tankettes, though they did not mass them in the German manner.

William Shirer claims to have seen the results of the "Horses against tanks, the cavalryman's long lance against the tank's long barrel."

When actually discussing it, the documentary does say "legend has it" that cavalry attacked tanks. That could be worse, I'll give it that. Max Hastings does argue that there are two occasions where Polish cavalry and German Panzers fought, though his account is jumbled. He states that "a squadron hurled itself at full gallop at the village of Kaluszyn, strongly held by the Germans" and that "out of 85 horsemen who attacked, only 33 afterwards rallied."

He finds an account mentioning lances from a distance from a Lance-Corporal Hornes who says "we saw new unfamiliar contours... agile horses with bobbing heads, ridden by Polish Uhlans in their khaki uniforms, long lances held with one end in the stirrup and the other slung from the shoulder... our machine guns opened fire." The film footage shows that this was riding formation and not necessarily attack formation since we can also see the carbines and grenades. It is also from a German account, and while we can't discount those, we have to take it as a grain of salt considering the nature of Nazi views on any Eastern enemies.

So, at best, relying on German sources, there were two times where this happened, and one was a small attack of fewer than 100 men on a town.

The most likely origin of this myth/exaggeration is the famous account of Krojanty on September 1st.

At Krojanty, Polish Uhlans in the number of 250 men were indeed ordered to charge in desperation... against infantry... AND THEY WON. They scattered a German battalion, only to be ambushed by German armored cars as they pursued. The armored cars cut down and scattered the charge, which again, was already in progress and was proving successful. News crews, famously Italian in one case, saw parked mechanized vehicles, dead horses with sabers and lances, and filled in the blanks.

So to sum up, was "blitzkrieg" and the 1939 Wehrmacht impressive for its time... well obviously. It beat Poland in a month! Does the documentary summarize Blitzkrieg into something that is a bit of an exaggeration without making connections to earlier or later developments... I would argue it does.

It isn't the worst source in how it covers Polish cavalry, but "legend says" and then regurgitating an old myth isn't ideal.

Sources:

Max Hastings "Inferno: The World at War"

Heinz Guderian "Panzer Leader"

William Shirer "Rise and Fall of the Third Reich"