Nintendo says this has never been a secret, they have just chosen to not talk too much about it as the unit was retired many years ago.
While Sony has made half-hearted attempts to invest in virtual reality, Microsoft and Nintendo have been even more lukewarm. That said, Nintendo isn’t totally opposed to the idea, and if we ignore the epic fail that was Virtual Boy, there was also the cardboard-based Labo: VR Kit in 2019.
