I have not seen any indication that Rowling, Musk, or Adams assert that trans people are categorically a "major threat". That said, these folks do view trans people as a "major threat" to those athletes who compete in the category that once was exclusive to humans distinguished by having XX chromosomes. They believe, and rightly so in my opinion, that this athletic competition category should remain exclusive to those humans scientifically established (usually pretty obvious at birth) to have XX chromosomes.