Every historian who suggest this is basically pulling it out of his ass. We have no evidence to support this. Sources on Hitler's early life and youth are incredibly rare and the only things we in essence have are his own account in Mein Kamps and the accounts of August Friedrich Kubizek, his friend in Vienna. Both are not wholly reliable because of their context. Other than that, the only accounts that surfaced of Hitler's time before Vienna were from people interested in gaining fame from knowing Hitler.

As I said, there is no evidence for that and therefore, everybody claiming this is pulling it out of his ass.

Also aside from that, chalking up the genocidal aspirations of a dictator to his own alleged desire for his mother seems like a cheap freudian ploy in a refusal to engage with the historical figure from a historical standpoint. Making Hitler and the Nazis out as mere psychopaths excuses us from critically engaging with them and finding explanations for their behavior.