It truly is

In most scenarios I would think that the amount of stress/hormonal manipulation required to make him lactate at all would not produce enough milk to even give a baby a snack let alone a meal, on top of which it would all likely be too poor of a quality to feed the thing in the first place

Women also have more fat deposits from which they make fatter milk (In most cases. This is only the case with brown fat (survival fat).). This is the reason women have more curves and differently structured fat-storage cells. Even if a man managed to procure enough milk to feed a baby, it would simply fail to give it the nutrition it needs.

Boys are just girls that aren't girls anymore? So a trans girl is a girl that's not a boy anymore that's not a girl anymore?

All vertebrates start out as females in the womb while all invertebrates start out as Male.