Frankly, if I were the BMJ I would start contacting lawyers and issuing writs. I'm unsure of
exactly what or
where or
how, but the principle that peer-reviewed scientific articles are being shadowbanned as "false" and unshareable by a for-profit, unqualified US organisation is...deeply offensive. A large lawsuit by an organisation such as the BMJ (an impact factor 40 journal first published in its current form in about 1840) would, at the very least, highlight how Facebook rapidly has become a publisher and its algorithms shape what people see.
It's like making a collage. If you put newspapers in a shop window, and sell them, you're a shop. You don't write the newspapers. If you cut out individual letters from newspapers and give them to people, you're not a shop, and you've made the message you create. Facebook is cutting out alternate sentences-to-paragraphs from the tabloids and selling a set of stories it thinks its users like, interspersed with ads. That question of degree is very much the sort of thing that legal brains like to get involved in.