Still waiting on confirmation of if Mori-san is a girl before celebrating the birth of a new yuri couple. They could just be a guy who notices the small details.
Mori has obvious boob curves, Okano calls Mori a girl... Mori could turn out to be a trans man but it seems an unlikely narrative direction.
Very likely a girl, but I have seen quite a few dudes with similar boob curves. I very much doubt it tho
Where do you live where skinny dudes have boob curves?
Where does OP live that a mangaka would represent a male person with boob curves just because some vanishingly small proportion of the real-life male population has some version of boob curves?
Characters are drawn with features that tell readers something about the characters—when a character has boobs and another character says of them, “She’s a girl,” and the author gives no indication that there’s gender-disguise or gender confusion going on, she’s a girl.