Although Da Vinci had church permission to do autopsies for the purpose of drawing the internal structures of the human body it was still very controversial and he had many enemies in the church and in government because of it.
If you come up with some proof that Da Vinci was gay instead of the usual homo-agenda BS I'd be interested in seeing it.
To be honest, I haven’t studied DaVinci’s life exhaustively. Apparently he was once arrested for sodomy - but the charges were dropped. The conventional wisdom is probably based on that, the fact that he never married, and that he seemed to like apprentices with feminine features. Obviously, that’s not conclusive - but suggestive.