I ask myself a similar question.
I suppose, for me, the number one issue is and always will be the environment. Our moral responsibility to the planet and all the species on it trumps everything, not least as there is little point worrying about any other matters when we could all end up dead due to global warming directly, or the wars over water and food that it will cause.
Beneath that issue, what is most important? Surely it is that all humans have access to basic human rights and a half-decent standard of living (UK 2021 this surely means a clean home, heating, internet, mobile phone, healthy food).
In terms of basic human rights then that is to a large extent protecting underprivileged groups from harm from others. GC feminism is there for the benefit of all gay people and all women, so it is fighting for a pretty damn large group. Not only that it is fighting for the rights of heterosexual men too (albeit those rights are not currently under threat, but could become so).
So yeah, Other than the environment and ensuring everyone has the basics then this issue is right up there, because it has nothing to do with a tiny minority of self-declared trans people, it is about the rights of everyone with a sexual orientation, not least women and gay men.