That doesn't make any sense. If the MC transformed from a male to a female, then any contact the MC had with other males would then be male on female...because the MC would, at that time, be a female.
Maybe there would be M/M content BEFORE he transforms into a female, but after the transformation, it would all be M/F...at least physically. Maybe he became a female, but his mind stayed the same, and he felt like he was being gay, just cause of his mind still being in male form, but then slowly comes to accept that it is ok, since he is a female now....and that is the majority of M2F games I've played. lol