Okay. The point is that if one has to appear as a given sex to be that sex, then conversely appearing as a given sex makes one that sex. It's inconsistent to simultaneously hold these positions:
Person A is a man because they look like one
Person B is a woman even though they look like a man
Person C looks like a woman but is a man because of other reasons besides appearance
Either appearance matters or it doesn't, either there is a clear definition of what makes someone a man or a woman or there isn't, but there can't be a definition that works however you need it to at the moment when you want to sort a given person into a category but doesn't apply to other cases.
You lost me on this, though.
My point, which I think is shared by many, is that there is a biological reality that makes a person a man or a woman. It has to do with sperm and ova.
(At this point, people often start to play language games that are along the lines of: Since seven year olds don't produce ova, it's ok for Fred to use the girls' locker room. I left out a few steps in the middle, but the arguments aren't really worth discussing, and the conclusion is absurd.)
"Appearance", by which we normally mean the way a person looks during normal interaction, i.e. with their clothes on, can often be used to infer their relationship to sperm or ova production, but its an imperfect method. In other words, "appearance" is not a definitive characteristic of sex at all, but it can often be used to infer sex. It does sometimes lead to inaccurate assessments.
So your reference to "Person A is a man because they look like one." is not part of any argument I've seen anyone make. If you are attributing that to me or anyone else on this thread, it's a straw man argument.
Where it gets a little bit confusing is that there are certain cases where most of us are willing to pretend that a man is actually a woman. Our willingness to do so may be correlated with the steps that they have taken to appear to be of the sex which does not match their biological reality.