At least in the UK, this became a matter of renewed public interest for two reasons: firstly, a proposed reform of the law to remove all gatekeeping from the process of changing one's 'legal sex', and secondly, an appalling case of several imprisoned women being sexually assaulted by a man (Karen White) who had been incarcerated alongside them due to having a 'legal sex' of female.
It was left-wing feminist groups, who organised largely offline to begin with, that reignited this debate. This wasn't some artefact of social media raging, it was a grassroots effort to halt and reverse a change in the law due to its clearly negative effects on women.
This is also a debate that has been ongoing for decades, long before social media websites even existed. Janice Raymond wrote what turned out to be a quite prophetic book on this topic in the 1970s, for instance. Renée Richards was stirring controversy in women's tennis at around the same time. Much of what you'll hear on this topic these days has already been covered by radical feminists for many years prior.