Fascinating tweet, and the reply above it. Not sure what this is "asking" but I guess I can add my thoughts. Yaoi and "femboys" tend to go together bc of the classic bishonen and cute styles, but a single femboy, in my yaoi estimation, does NOT a yaoi make imo ..there needs to be movement, a dynamic between two, a push and a pull, hence the classic Seme & Uke narrative designations. There can be a dynamic between a beautiful boy and the audience, and that is still a push and a pull, which CAN be yaoi, but imo I guess is more for the yumejos and that's not my area of experience or relation. A single "Femboy" (regarding how ppl use it for fictional characters, not self identification of irl ppl) my impressions on the internet seems to be related to a lot of more specific body shapes and youthful fashion aesthetics rather than a character or dynamic on its own.

Regarding fetishized femininity, that's definitely a part of it and a part of Yaoi, though that probably imo is just something that is part of the kink. Many het romances explore an eroticized version of restrictions and oppressive forces on female sexuality, and a lot of classic yaoi tropes basically copy those but translates them onto male uke characters, sometimes without even changing much about the gender dynamics! . Many fujos do like it for the "distancing" from ones own relationship to femininity and irl sexism, or just a way to enjoy hot tropes but with cute and young guys. Or sometimes not even necessarily with "feminine" guy characters, but putting objects of fan-love and desire into that objectification-chair to be aggressively rained on with affection that gives them that quality (the "babygirl" phenomenon)