many aspects are irreversible, basically anything that happens to your skeleton cannot be undone. there is no surgery to remove my pelvic tilt or make my hands bigger, i just get to live with them for the rest of my life (this is as a result of estrogenic puberty)

edit: was busy earlier but thought it would be beneficial to elaborate on this

for all trans people, skeletal changes during natal puberty will often be irreversible; this includes general lengthening and thickening of bones for a natal-testosterone puberty, and a lack of lengthening and thickening of bones for a natal-estrogen puberty (late testosterone 2nd puberty can thicken bones, but not lengthen them, due to the fusion of the bone plates that make growth possible). this means that e.g. on average, trans girls will be taller than they would otherwise be, and trans boys will be shorter. idk if you’re aware, but height changing surgery is massively expensive and risky, so practically speaking, changing it is impossible

there’s nothing for hand size for either direction of puberty either. again, on average, trans girls will get bigger hands than they’d otherwise have, and trans boys will get smaller hands. as far as i’m aware, there are no surgeries for hands, which is probably good because they’re pretty densely complicated pieces of biological machines

i believe trans girls can develop the pelvic tilt after estrogen (?), but no widening of the pelvis itself will occur. similarly, there’s no way for trans boys to reverse their pelvic tilt nor narrow their pelvis

also, trans boys can get facial masculinization surgery, but there are limits to what it can do (e.g. brow ridge)

none of this touches on how “technically reversible with surgery or hormones” is an awful bar to hold for allowing a trans kid to go through natal puberty, but i’m hopeful that you’re in agreement with that and it doesn’t need to be spelled out