'I'm genuinely interested in why there is a sense that trans people are subjugating cis women?'
I've never seen this phrase used before. Subjugating is not a word I would use. I also wouldn't group all trans people together like that. I don't think eg non binary teen girls (female) are subjugating anyone!
The issues as I'm sure you know, being a life long feminist. Are this sort of thing-
Historically female only things being opened up on a self ID basis.
The refusal to engage with women and girls on what the consequences could be, why women and girls are worried, are there other solutions etc. Women and girls who ask are called all sorts of things and disregarded.
The removal of the ability to have any word/s to describe women and girls as a group. The new language reducing us to body parts- which due to the nature of the situation are referencing our sex/ reproductive organs. This has many many issues here and around the world.
'trans people' are fighting for what they want, most I'm sure are not actively thinking of ways to subjugate women.
The fact is though that the... Philosophy? Political stance? Is totally inconsistent. With what words mean what and what is transphobic shifting continuously. How can important policies be dependent on words that mean different things to different people?
A lot of what's being pressed for is a gift to MRAs, incel types, and the large minority of men who enjoy upsetting, scaring, unsettling, sexually assaulting etc etc women and girls. And all those who think women need bringing down a peg or 2.