Wrong.
It depends on the puberty staging the girl was when commenced on puberty blockers.
If commenced at Tanner stage 2, as desired and recommended by gender clinics and WPATH, no fertility is developed. Ova maturity happens in the later stages of puberty. Without oestrogen the eggs cannot mature. Girls are sterile.
Equally the vulva, vagina and uterus does not mature. They cannot have sex and the uterus is incapable of carrying a fetus.
If puberty blockers are commenced at Tanner stage 2, there is only breast budding. There is no development of breast tissue to breast feed. Which is immaterial because they’re never going to have their own baby.
The cessation of testosterone is only relevant to those whose bodies reached a level of pubertal maturity - periods - before it was commenced. For those that didn’t, ceasing testosterone won’t improve fertility. And then there’s the effects of testosterone on the vagina. Atrophy of the tissues. Assisted technology is often required to help get pregnant, thus meeting the criteria for infertility.
Only a complete cessation of puberty blockers with instigation of female puberty will see these issues resolve. If young enough, puberty may resume on its own. But once past a certain age it won’t. Exogenous oestrogen would be required with questionable success rates.
I hope this helps some of your gaps in knowledge.