J.K. Rowling is continuing to add to Harry Potter canon and, more specifically, Albus Dumbledore's sexuality, by divulging further details about his relationship with Gellert Grindelwald.
Rowling famously revealed back in 2007 - after the final book had been released - that Dumbledore was secretly gay, and had been in love with Grindelwald when they were young. With the Fantastic Beasts franchise including both characters, it had been expected that it'd delve further into their relationship, but again The Crimes of Grindelwald only had hints and suggestion of Dumbledore's feelings for his former friend. Speaking on one of the special features for the movie's home release, Rowling says (via Radio Times):
"Their relationship was incredibly intense. It was passionate, and it was a love relationship. But as happens in any relationship, gay or straight or whatever label we want to put on it, one never knows really what the other person is feeling. You can’t know, you can believe you know. So I’m less interested in the sexual side – though I believe there is a sexual dimension to this relationship – than I am in the sense of the emotions they felt for each other, which ultimately is the most fascinating thing about all human relationship.”
This confirms that Grindelwald reciprocated Dumbledore's feelings, and that they had sex, but it's also another case of Dumbledore being 'Schrödinger's gay', since Rowling saying "I’m less interested in the sexual side" is her get-out clause for future movies not really showing much more of their romantic relationship. It's one thing for Rowling to keep addressing these things in Q&A's or commentaries, and quite another to, y'know, actually put it in the books or movies.