When (as a physical scientist/mathematician) I used to sit on one of my University Research Ethics Committees, I once pointed out that saying sex/gender given the current issues was not good enough. If they meant sex, they should ask for that. course, depends (not that I can recall now), if it was medics/biologists or social scientists/psychologists, and what precisely they wanted to know.
" I would just like to ask what is your sex, but I don't think I will be able to do that."
Why not? If some wokey discipline, I would expect they already have a standard form of include all six billion genders and don't offend anyone. If you mean sex, then you need to say that, in whatever way makes it clear you mean sex. I would find adding sex assigned at birth to a biologist etc to be misleading and frankly wrong.
Have a sex question and a gender identity question if you really need to, just to make clear you are distinguishing between the objective and the subjective.