The existence of Transcendents, in a certain sense, was actually no secret.
Although everyone maintained a low profile and secrecy, in reality, there were quite a few people in the world who knew about the existence of Transcendents.
Governments and government officials and aristocrats around the world were more or less aware of some facts about the existence of Transcendents, while there were also some related stories that circulated among the general populace.
However, according to the covenant signed by Transcendents from various countries after World War II, Transcendents were forbidden from publicly displaying their Supernatural Powers before ordinary people.
This was partly to conceal the true nature of the existence of Transcendents, to avoid unnecessary social panic and unrest, and partly to maintain the mystique and transcendence of the Transcendents themselves.