Hasn't denied it either.
Gänswein initially began his seminary training at the International Seminary of Saint Pius X in Switzerland. This was finally reported in 2009 by French magazine L'Express. No one at the Vatican has ever officially denied it. A two-year gap in the biography of Gänswein suggests this earlier seminary training was certainly a possibility. -Wiki
No, they haven’t, but they haven’t confirmed it yet. It’s just a rumor. If they haven’t confirmed it, it’s not true, or it’s a terrible secret the public can never know.