So I think there's three things:

1. Being against current trans ideology - I don't think this has anything to do with religion or not it's literally about not engaging in an orwellian level of reality-ignoring where a giant cult gathers together to shame and harass anyone who doesn't loudly chant that the sky is yellow and the grass is red. Thats why right and left wingers outside the cult can mutually agree on this point. (like, you can say that religion and atheism disagree over basic facts like "is there an invisible god" but its not like religion is standing there proclaiming that there's a completely visible god standing right there and everyone can see him and if you claim you can't see him it's because you're a lying, hateful person who is literally a murderer)
2. Being gender critical, ie opposing associating gender roles with sex - some religions have stronger gender roles than others. I have not found this to be an issue for me personally with my own religious choices, ie I've felt comfortable ignoring gender roles (religiously. societally, I've felt discomfort/social pressure that I needed to overcome).
3. Radical feminism - opposing all structures of the patriarchy - outside of religions that are explicitly female centered like some modern branches of wicca, pretty much all religions have had too much shaping in the hands of misogynist men through history to not be full of things that are problematic from a radical feminist perspective. To be religious and a radical feminist is a contradiction. However, it is a contradiction I live with by compromising on both instead of being ideologically pure to either. My religion is full of misgyny that I sidestep/avoid rather than dumping the religion entirely as an act of protest (I mean the most radical of radfems would say the same thing about engaging in heterosexual relationship. I cannot call myself a pure radical feminist because I am simply not willing to be radical enough... Whereas I'm comfortable calling myself fully gender critical.)