The estimates are 10% to 15%, which seems rare enough.
However, these are medical detransitioners; that is, people (mainly young women) who drop the hormones or look for cosmetic surgery to repair the damage.
What nobody seems to mention are the "social detrans," the people (again, mainly young women) who cut their hair, wore chest binders, changed their names, and led life as the opposite sex for several years, and then changed their mind to resume what they could of their natal sex.
One of the reasons "affirming care" seems to work is because it's easy to get along when you're surrounded by people telling you that you are special, that you're brave, and who make accommodations for you. Family and friends make it easy to Trans when you're a teen because they are affirming your decision daily.
Unfortunately, many of those people get out into "the real world" and have a difficult time without the constant affirmation. They begin to question their decision, and in the absence of frequent affirmation and support, quietly go back to being girls or boys (really, young women or men).
I've been searching for good numbers on these quiet detrans, but if they were not getting any (or very little) medical care, nobody seems to be recording them.