From your linked paper, jj1968:
Transgender women experience muted Tanner stages. There is an initial development of a subareolar breast bud at 3–6 months followed by further enlargement and development of the breast. Maximal breast growth is realized at 2–3 years in our experience. Figure 1 shows heterogeneous breast tissue in a mammogram from a transgender woman treated with cross-sex hormones. Breast size and tissue composition following estrogen treatment varies for each individual. [9•] Transgender women are unlikely to reach Tanner stage 5 [6] The degree of breast development seems to be independent of type and dose of hormone treatment.
The authors and your quote also refer to "pseudo lactation", which means the production of fluid (usually a milky discharge) from the nipples unconnected to the milk produced in breastfeeding. This is normally referred to as galactorrhea and although more common in women and girls, can happen in men and boys. Where this occurs naturally in males, it is always pathological and the cause must be investigated. It can also be a side effect of various medications.
What it is not is proof that the individual in question has mature breast tissue capable of feeding a baby.
I would highly recommend reading up on lactogenesis (what changes in the breast are necessary so that we can feed a baby). Given that completed puberty is necessary, that the brain (specifically the pituitary gland) sends out the signals stimulating the maturation of breast tissue during pregnancy and that breast development is only complete after pregnancy and labour, I would need to see actual evidence before I will ever believe that a male can breastfeed. The paper I have seen so far does not even suggest that the male in question reached stage 2 of lactogenesis (i.e. copious milk production). And that's before we even get to the lack of any data provided about nursing after the birth of the child.
Here is an informative science paper explaining the physiological process of lactogenesis:
www.ncbi.nlm.nih.gov/books/NBK499981/
As the onset of lactation involves sensitive changes to progesterone, insulin, cortisol and prolactin, thyroid hormones, hormones coming from the placenta, oxytocin and estradiol, it can prove difficult to induce lactation in females who have never been pregnant. Not all women seeking to induce lactation in this way succeed, but many do. The numbers who induce lactation AND produce milk levels similar to women nursing after childbirth is much smaller though.
However, because the physiological changes to a female's breast tissue remain after weaning, it is much easier to induce (re)lactation in cases where the woman has been pregnant before, with the best success rates for those who have nursed previously.
And here for instance is a study of the composition of the breastmilk produced by non-pregnant women:
pubmed.ncbi.nlm.nih.gov/25288606/
Please note in both study subjects the maximum amounts produced daily did not amount to even one feed. Milk composition was markedly different to that produced by mothers after childbirth (but not in a way harmful to the baby), but they did not analyse the milk for levels of the artificial hormones the women took to induce lactation.
As the authors note, the composition of breastmilk after childbirth has been studied in detail, as has the effect of hormones and medication on the same. There is however very little or no data on the effect of hormones and medication on the milk produced after induced lactation (as the authors point out, given the small amount of milk produced, changes in composition may happen) and on the overall composition of the milk. That means we cannot simply assert that because levels are not harmful in women who are nursing after childbirth and in those who establish a normal supply with the help of drugs after childbirth, the levels will also be safe in women who have not given birth where the amount of milk produced may be significantly smaller.
As such analyses are necessary to assess possible negative impacts on the growing child, the authors urge that more studies like theirs should be undertaken in cases of lactation induced without pregnancy.
Consequently, it would also be the responsible course of action to analyse the milk - if any - produced by males inducing lactation in the same manner that these other studies have done. Until I see an expressed willingness to undergo such scientific analysis by these males and their doctors, with an independent lab comparing samples on at least a weekly basis, I must assume that the wellbeing of the child is not the primary motivation behind inducing lactation in such cases.
(There is in my view nothing wrong with adoptive mothers seeking to induce lactation because they wish to experience nursing in all its benefits for mother AND child, but the fact that breastmilk is considered the best way to feed a baby is usually the driving factor in attempting it.)