My understanding is that (some) transmen want to have children, but be fathers rather than mothers. My objection to that is not on an individual level - the desire to procreate exists in men and women, trans or not - but in the 'Look at me! I am a man and also pregnant!! And I exist!!!' attention-seeking approach to the situation. The reality is that this is a woman who is 'living as' a man (whatever that means) and despite that is pregnant, which is only possible because of being female.
Nobody is likely to have said that this person doesn't exist. The idea that anyone would think someone else doesn't exist is in the minds of the trans lobby - it is blindingly obvious that someone standing before you, or in a photo exists, so the trope makes no sense to me at all.
Also, the notion that a man can conceive, carry and give birth to a baby is ridiculous. There was some confusion on here a while ago about advice supposedly given to midwives about men giving birth. People seemed to believe that this was genuinely about actual men, when it seems obvious to me that it referred to transmen whose sensibilities are too delicate to have their sex mentioned, even in the throes of that most female of activities - giving birth. The gaslighting insistence on not 'misgendering' people results in confusion and misinformation, and is not based on reality in any way.