This is an evolving area. There was a Tax Court Case in 2010 that ruled that gender identity disorder is a real disease, that hormone therapy and gender reassignment surgery was a deductible medical expense, but breast augmentation was not deductible, because it was cosmetic to approve appearance only. (Although the articles don't use the term, it seems that "bottom" surgery is deductible but "top" surgery is not.)
https://taxprof.typepad.com/taxprof_blog/2010/02/tax-court-gender.html
https://www.journalofaccountancy.com/issues/2010/may/medicalexpense.html
It would have to logically follow that de-transitioning is also a deductible medical expense in general, and some parts of the treatment would be deductible, but that removing the breast implants would likewise fall under the definition of cosmetic surgery.
However, it's worth noting that this was 13 years ago and the Tax Court was deeply divided on the issue, with five minority opinions agreeing or disagreeing with various parts of the ruling.
I would have to say that, under the current law and court cases, removing the implants for detransitioning is not deductible, but it is probably ripe for a new court challenge. However, that is a long road to undertake, and probably expensive, if you wanted to push the issue.
