Are the "documentaries" about the nazis developments and future inventions true?

Short answer: no.

Long answer: The Nazis did, in fact, spend a portion of their budget on weapons and technology that, while not as dramatically advanced or otherwordly as the entirely apocryphal "Glocke" flying saucers, were next-gen by the standards of the time--an amount that increased as the war went on and the Germans became increasingly desperate for some kind of superweapon that could stop the Soviet advance. A lot of that research did produce useful results, but there simply wasn't enough time to develop practical battlefield applications for these breakthroughs, and most of the technology developed for Nazi wunderwaffen only became expressed decades later, in the arms and doctrine of the former allies.

In Stalingrad, for example, one of the biggest small-arms advantages Russia had over Germany was the proliferation of a rugged, cheaply produced SMG called the PPSh-41, which proved far more useful in cramped urban combat than the battle rifles that both sides relied on at the time. The Germans had submachine guns too, but the MP-40 was more expensive to make, originally issued only to military police and SS officers, and was harder to control due to its more powerful ammo. By the time they withdrew from Stalingrad, the Nazis knew the battle rifle was a liability in asymmetric warfare, and that what they needed was a smaller, more maneuverable rifle that could be used at short range.

This led to the invention of the assault rifle, a selective fire weapon with a medium-power cartridge that's still the standard for soldiers all over the planet. The StG-44 was exactly what the Nazis needed, and even today, elements of its design are so ubiquitous that you can Google it and think "Wow, that's the assault rifliest assault rifle that ever assault rifled!" It even came with gimmicky attachments you'd expect to see Richard Machowitz playing around with, like the Vampir night vision system--also the first military application of the technology--and a cornershot attachment that basically consisted of a bent barrel and a little mirror. But not only did it come too late to make a tremendous difference, but as the first of its kind, it had many bugs to work out. It was stamped metal, hard to maintain and nearly impossible to get replacement parts for, and the revolutionary new cartridge was a proprietary design that could only be acquired through rapidly disintegrating Nazi supply channels.

Whenever American experts of the time talked about German arms, though, you find that it took us a long time to even understand what they were trying to accomplish with this thing. We were already butting heads with the Russians, you see, and we were so keen on pretending that we'd beaten the Nazis single handedly that we mostly forgot that Uncle Joe Stalin was ever one of the good guys. This silencing of the Russian side of the story meant that we didn't learn the lessons that Germany did--which is why we were still using battle rifles well into Vietnam.

Other botched Nazi superweapons that later popped up in our armories included the long range rocket--which regularly missed England in its earliest incarnations, but which eventually landed us on the moon.

On purpose.