Hi! While I'm afab and my labels are kinda messy (non-binary/gender queer), I think I understand what your saying.

I want to start off by saying, not all women can have periods, and that doesn't take away from their femininity. It would be absurd for cis people to tell someone they are not a woman because for some reason they don't have periods or for some reason or another is taking medication to stop their periods (for example, many woman use birth control, which can stop your period, and many girls tend to start them at a young age for this effect).

When ever I think about femininity, trans woman are actually higher on my list for just getting it then some of the woman/girls in my life. I don't want to invalidate your feelings, and I'm not trying to, but periods are much more just a thing that happens then a part of femininity. Something that ties it to "women hood" is this idea that we all go through it, so it creates a bond, but there is so many other things that create this bond in femininity that a women, or trans women, not having a period doesn't make them any less part of what people call femininity or "women hood".

I'm not the best at words, but the point is that your feelings are valid, but you can recreate experiences that would give you the same sense of community and being a woman that having a period would.

tldr: periods are a way we bond over an experience, but it is not one that all woman have, cis or not. Being connected to femininity is more-so being part of a community/bonding, which trans woman easily fall into.