I am gender critical and have been horrified by the whole shift towards 'birthing people', 'pregnant person' and 'chestfeeding'. Talk about minimising the unique and special role of women!
However, the idea of men breastfeeding definitely isn't new and has always been technically possible (men have milk ducts although far less of them), although it is vanishingly rare. At university I had a very tedious summer job involving categorizing articles in medical journals and one day came across an article about induced lactation which gave a case study of a man lactating in order to feed a baby, although to a limited degree. I remember that I found it fascinating and read out paragraphs to the rest of the office! This was back in 1994 and the article would have been published around that time (as we categorized recent journals as they were printed), although I cannot for the life of me remember which journal.
Many years later I became a breastfeeding peer supporter and along the way learned about re-lactation, mostly via domperidone and pumping. Sadly this was quite a common query on the helpline as new mums often hadn't been given proper support in the early days, had given up and then wanted to get re-started a bit later down the line. This can also be done using a re-lactation device (basically a tiny tube leading from a formula milk supply - the tube can be taped to the side of the breast so that baby latches on, receives milk via the tube and the breast is simultaneously stimulated to produce its own milk).
Induced lactation is a much bigger thing in the USA due to the higher rates of newborn adoption and adoptive mothers then wanting to start breastfeeding. Also for surrogacy arrangements. It is the same process as relactation (domperidone, pumping and using a relactation device), but much harder work as the nursing mother hasn't given birth and had the hormonal changes that help to kickstart the milk supply.
So the idea of men feeding hasn't just come about via gender identity politics - it is already known although very, very rare - however if it is used as the main means of feeding a baby it raises significant ethical questions. The main issues seem to me to be the risks of drug transfer via the bloodstream and the interruption to the milk supply of the mother, if the baby is not feeding from her.