Sounds like someone is supporting law breaking and despite (ridiculously) needing to be told what a female is by the highest of courts, is still a reality denier.
1. Females are not "assigned" a gender at birth as though the doctor/midwife cannot fathom what they are and randomly picks a gender from the available genders list, they observe the gender and record it.
2. Trans women are men so are participating as men, in much the same way as someone who dresses as a pirate or dinosaur in the marathon isn't really participating as a pirate or dinosaur, they are participating as human females or human males. So long as the pirate doesn't steal from other participants and the humans pretending to be dinosaurs do not eat the other participants then there is no problem with this.
So long as their time doesn't get recorded as a female and is recorded as what they are (male in the case of man dressed as woman) then this is no problem. Lots of people wear fancy dress to the Marathon and if men want to dress as women for this as a costume then that is fine, as long as (should they need a toilet break) then they use the male toilets if they are a man dressed as a woman.