I'm a little unsure what you mean. I am a trans man, that is, a biological female who has had medical intervention to make my body appear more like that of a male. Do you mean if I had been a trans woman (a biologically male person)?
In terms of being an ally, I think I am probably less informed than someone who is openly trans or does not pass. However, what was helpful to me early on was simple compassion. I know it is something that seems very odd and is hard to understand for your average person, but when people are willing to let that go and treat you first as a human being entitled to dignity, any other barrier can be overcome IMO.
I did used to have mixed feelings about the increased awareness of trans issues, as it did make me more fearful that someone would spot something in me. However, those fears have alleviated somewhat over the years, as I haven't had any issues for a long time now. I hope it will help younger trans people be kinder to themselves, and to live an easier life.
In terms of the GC movement, I have found it isn't homogenous. I have seen people who have a clear disdain of trans people, and who go out of their way to be hurtful and cruel. However, there are also concerns that I can understand and identify with.
I share the concerns about people being pigeon holed and stereotyped by the biological sex. I worry for people who undergo medical transition for social reasons, rather than sex dysphoria. I don't agree with any attempt to delegitimise their distress, but I wouldn't want to see people make changes to their body that they will live to regret. I know how much sex dysphoria can blight a life. That said, it may be that medical transition is the best way to relieve their distress, and who would am I to say they shouldn't? Ultimately, I don't have easy answers on how to balance these genuine concerns with the risk of doing harm by limiting peoples' agency.