Ryou's gender is unequivocally male to me. He doesn't necessarily seem like the type to conform to hard societal gender norms, but that's personally just how I feel!
I don't think it's necessarily because he grows his hair out either. I mean there's nothing wrong with a boy that's got long hair. I think it's more...in his mannerisms.
Jonouchi is a good example of his opposite, actually. Loud, brash, super extroverted, lil self important. Ryou is the opposite in that he's quiet, pragmatic, and personally I think TTRPG is a very introverted game style. He's also not terribly self important, aside from thinking he's the boss at boardgames and tabletop shit.
Literally one of the first things you hear from Ryou (at least in the english manga, I'm not sure if it translates over that way in Japanese) is that he's "not good with girls"
Most of his positive interactions are with his friend group, which includes Anzu, and he's comf with her, for example! It's all a matter of perspectives, and being idolized for his looks is probably really not fun for him.
That being said, I feel like Ryou could swing either way. He seems like he'd be just as happy with a fella as a lady, so long as he's attracted which HAHAHAHA WHAT.
as an endnote to this while I do like the idea of him being bi, his discomfort with girls and the way they idolize him might make him more wary on that end. He knows he has a pretty face and girls like pretty faces but that's not all he wants to be known for.
Ryou is the opposite in that he's quiet, pragmatic, and personally I think TTRPG is a very introverted game style. He's also not terribly self important, aside from thinking he's the boss at boardgames and tabletop shit.