I think this is a discussion that will be allowed by chess.com. Organizations are quick to censor controversial topics but I think there must be a pushback against nonsense of any sort.
Ok, but "this nonsense" isn't happening. You're asking about a hypothetical.
Well, It will be interesting to watch what actually happens but I think they will not allow that man to play, I think while registeration of FIDE account they see the birth certificate to clarify age, gender etc. So, they will be knowing this is a male and simply wouldn't allow him. But, a real transgender in chess would be taken in male or female idk, probably female.
There is a small problem with that though. In our state, anyone is allowed to modify their birth certificate to reflect what they happen to feel at the moment. So if someone is born male, but later feel like they want to be female, the birth certificate will say female. Or it could say neither.
So checking a birth certificate wouldn't be a means of establishing if someone has XX or XY chromosomes. And even if a dna test conducted determined if someone was male or female, what about disorders like XX males or people that are XXY?
Then, the FIDE official will have doubts and will recheck is he male or transgender or done some surgery, then they will know if he has done surgery looking at certificates.