Yes, I think I agree with most of this.
Yes, digital id should be optional.
Yes, if you opt to have your sex on your optional digital id, it must be your actual, birth sex.
Yes, if digital id becomes required to prove that you are eligible for that particular single-sex service, anyone who chooses not to add their actual, birth sex should not therefore complain when they can't access that service.
However, given that it is likely to be difficult for some women to prove their actual, birth sex (see my long rambling previous posts):
No, digital id should not be required for female human beings to access female single-sex services. No woman should be forced to forgo access to female services (healthcare, rape crisis, intimate care ) because of national or international bureaucracies.
No, I do not believe that the default should be women having to prove they are women. We are in this mess because of a lot of (being polite) grabby men. Let them prove they are women, using their original birth records.