The undercut has existed forever lol, like for hundreds of years with the Vikings and even within African cultures. But undercuts that are relatively long on top are more of an indie, skater, punk, LGBTQIA+, or just general counter culture thing. I cut my hair that way up until very recently, and probably will do it again if growing it out looks bad. The undercuts that are relatively short on top are more associated with the fash (fash assholes with toxic masculinity brain probably think it's gay or unmasculine to grow the hair long on top) For me I don't care about people's haircuts at all unless it's something obviously reactionary like a swastika shaved in the side or something. Just let people express themselves and cut their hair how they want.
It's been a thing with the plaid and bearded for a while. We called it the Hipster Youth haircut at work
Since when did it earn the Hitler Youth nickname? I know it's popular with fash but wouldn't it just be called the fash-cut then?