Given the way things are I don't think we should expect current athletes to speak up
It would be hugely risky for an individual athlete to speak out, but I hope some will consider collective action, such as demanding the authorities review the rules, or even boycotting events in which male athletes are competing.
That actually happened in NZ last year, when a male downhill cyclist who had been competing without distinction in the men's competition was allowed to switch to the women's with 3 weeks' notice. Apparently, most of the female competitors refused to take part in the race. I say 'apparently', because the media deliberately misrepresented what happened, calling it 'confusion' rather than a boycott and then focused on lionising the stunning and brave translady (who won, of course). The only news we got of the boycott was a coy line buried in an article about said STABTL ('It was a small field for the elite women's championship race, with just five starting riders').
Still, given the way the conversation has shifted recently thanks to Martina's intervention, I think a future boycott would have more chance of getting coverage and with collective action it would be harder for the media to demonise any individual or for sponsors to abandon all of them.
The other alternative is for coaches to lobby behind the scenes. Of course that's tricky because of the competitive nature of sport - you just end up with the coaches of the team or country which features the SABTL lobbying hard in the other direction. That's what happened with Laurel Hubbard: Australian coaches made a concerted effort to raise the unfairness of Hubbard competing against females with Commonwealth Games officials, while the NZ coaches of course argued that Hubbard's inclusion was totally fair, nothing to see here folks.
Ultimately you would hope (although maybe this is too optimistic) that coaches and athletics officials would realise that whatever the short-term advantages of having a Hubbard or a Mouncey on the team, long term their presence can only be detrimental to the sport as a whole, because fewer and fewer girls and women are going to bother with training for and competing in events where they know they will be at a massive disadvantage.