The French film/play "Le prénom"[0] explores the idea of a contemporary father who wishes to call his soon to be born son Adolphe. Very interesting if you get the chance.

[0] https://www.imdb.com/title/tt2179121/

Mostly they changed their names, but there were never very many Hitlers to begin with. That’s part of why those who had the name faced such a stigma. If his last name were Müller, there wouldn’t be a stigma for having the same last name.

I had a friend whose family changed their last name from Hitler. Very few people knew their secret after the first generation with the new name.