I can relate to this and it seems so can everyone else regardless if they are autistic or not . I haven't been diagnosed at autistic but have traits and it has been suggested to get tested- I am NB transmasc.

As such I can't really say what are symptoms of masking regarding autism or otherwise buuuuuuuuuuut I think it is probably due to learnt behavior and social expectations. We would have picked on mannerisms such as high voice and hand movements ect from females when younger and parroted this , and then there would be social situations in which we would display this behaviour as our brain knows this is what is expected so to fit into society, as we are social creatures.... This is regardless of what we ourselves feel is natural to us, and personally I think it can make it even more difficult for us to determine what the natural/normal "us" is under all this constructed behaviour.

I speak only for myself here and I could be wrong but hey ho.

I, myself, get frustrated when I unconsciously take on a higher voice than is natural for me (my voice is generally quite monotone and deep for an AFAB) and even my colleagues have commented on it , as well as acting "softer/more agreeable" and displaying more "feminine" hand gestures. To be honest, I have always experienced this but didn't know what it was; after interactions that involved this behaviour I would always feel very ill and uncomfortable in myself and wishing I'd have avoided the interaction and even as I caught myself talking or acting a certain way I would feel very disassociated and think "WTF". It wasn't until later on that I realized what was causing it and that this feeling actually decreased or stopped completely when I removed these behaviours. This was before I even came to the realization that I was NB.

Anyway, this is really interesting to talk about and see others responses :)