https://www.bsuh.nhs.uk/maternity/wp-content/uploads/sites/7/2021/01/MP005-Perinatal-Care-for-Trans-and-Non-Binary-People.pdf
This is part of their maternity protocols for perinatal care. In the Infant feeding section:
"5.5.7 Non-gestational parents may wish to participate in feeding their
infants using their own bodies. Cis women who have previously breastfed may have the most success in relactating. Trans women and cis women who have not been pregnant may also be able to induce lactation to some extent. Methods for inducing lactation include using galactagoues and physical stimulation. Alternatively, some families choose to use supplemental nursing systems with expressed milk or formula."
They cite this website in the reference list: http://www.milkjunkies.net/2013/05/trans-women-and-breastfeeding-personal.html
Notably they do not cite any source which has tested the composition of any such male secretions for safety and nutritional value.