She's not gay out of nowhere. There are a few hints she's into it, and the male love interest is treated more as a joke throughout. However, it isn't developed well and her interactions with Yuki are still mostly played for comedy.
This series would be best with no romantic conclusions, and if anything a strong bond between Miyaji and Yukimori. Throughout the series they're the two characters with the most heartfelt, earnest interactions, and they barely interact in the final chapter because Watashiya was like "FUCK IT" for this chapter. It's a shame, because a platonic friendship between the two of them being the finisher for this series would've been unique and very interesting. Well, it was mostly unique throughout so I already had that. I mean, at least we had chapter 23 for that stuff, but 24 feels like utterly flaccid.