David Glantz is basically the best source on the eastern front in ww2. He's written a ton of books about it using primary documents and stuff.
Also I swear there was another video with better quality but i can't find it
also don't expect him to be an ML or anything he was in the us army but that doesn't take away from the fact that he basically just uses soviet primary documents to write his books
Yeah he ain't an ML or anything but he has been critized by some western folks as being too kind to the soviets. Of course he has also been criticized by russia for talking about some of the soviets failed offensives