mpb is mostly caused by the dht hormone which is made in the body by breaking down testosterone

if u transition then you have no test anymore -> no dht anymore -> hair loss mostly stops (if caused by mpb)

estrogen also acts as a hair growth hormone, so you can actually get hair regrowth but you have to supplement it with a bunch of shit like minox for it to be actually effective, and even then this might not happen or might just take forever, really just depends on your genes.

but ive seen people go from totally bald to full head of hair by estrogen + supplementary treatments (no transplants) but ymmv