I have sometimes wondered if, just as God permitted the impact of The Fall to eventually give rise to birth defects such as cleft palate, bowed legs, congenital heart disease, etc….Would it not be possible for The Fall to also be reflected in a mismatch of brain and body?

The fact that God is neither fully male nor fully female is, yes, another interesting consideration.
Also, angels (according to many religious traditions) have no sex or gender, even though Michael and Gabriel have male names. As far as I can see, however, the scriptures don’t specifically state that they have no gender or sex. It states that they do not marry or reproduce. This doesn’t necessitate that they don’t have a gender or sex. They completely can. But it’s left without being addressed, so we don’t really know the answer to this.

I feel as though our witness to Christ has been enhanced by the unconditional love we’ve shown our child and by using their desired name and pronouns even though we did tell them we don’t really understand it all. We know other Christian parents who refused to use their trans child’s desired name and pronouns, and the child has gone no-contact with them. It’s very likely these adult children have no other Christian influence in their lives when they write off their family. We are able to speak of and glorify Jesus when our child is with us. Who knows what may come of this?

We wish there was a guide within the Bible to specifically tell us what to do, here. In the absence of this, we’ve chosen the expansive version of God Who reaches out to society’s “unloveables” and marginalized people. Trans people struggle to get jobs, and therefore, to be able to pay rent and buy food. It is an awful way to have to live. The ones who live like this as adults (beyond their teens) are giving up a lot in order to identify this way and for them, it isn’t a fad.