Breast tissue is just that, however brest milk is so much more. A woman's body changes the milk she produces depending on the needs of her child, if they are ill her milk changes to support recovery. Her body knows when to change milk so that a baby can be fed until and beyond weaning. There is very little chance that we could replicate this complex process completely. Yes, wecan use drugs and pumping to stimulate a milk substance, anyone can do that, male, female or trans! However the clever bit, the but that biology leads is so complex we don't even understand it yet. But we do know that lots of drugs pass into milk and that lots of drugs are never good for babies. It would be completely unethical for a transwoman to donate milk whilst we are unsure of the impact of the cocktail of drugs taken.
As for a transwoman settling a baby with breasts, you don't need to be producing milk at all, your nipples are biological dummies babies settle (sometimes) with a dummy in their mouth.
Totally unethical and definitely child abuse if anyone is taking a cocktail of untested drugs to support body changes to priduce milk.