I’d assume “FEX” in the last tweet in the OP is referring to this: https://github.com/FEX-Emu/FEX

Not as many as I’ve had with knowing. Piece of shit never works right.

there’s no fair use/dealings defence of them.

The OTW, who run AO3, would disagree with you: https://www.transformativeworks.org/faq/#faq-WhydoestheOTWbelievethattransformativeworksarelegal

That said, I’m not sure why they say ‘transformative works are legal’ rather than ‘transformative works are sometimes legal and we believe noncommercial, transformative fanworks are legal but no one has actually tested it in court and it’s unspecified in the legislation’.