This phrasing you quoted is wierd, so whoever wrote it must think they mean that there are more then two sexes, because even small children at school these days know that there are 9 million different genders to pick from..
Not sure how seriously you are asking this question. A job is a job. Your financial security and your career trajectory matters.
Only you know what other job options you have, what this particular job means for you and how much this aspect of it might affect you, or how much scope in your role you might have to try to change this policy if you took the job. Some of that you couldn’t know without taking the job anyway.
From my own personal experience, workplaces embracing this agenda tend to be sexist in other ways, but equally companies who don’t even think about genderism can be sexist as well, and some you wouldany expect can be quite pro-woman. And workplace culture comes from colleagues as well as leadership, though leadership is fundamental to giving the steer.
I’d say workplace sexism is rife (particularly evident if you have kids at home, which you haven’t specified) so we all need to be ready to stick up for ourselves, campaign where we can, move jobs to look after ourselves, keep our heads down, whatever we need to do at work.
I look up a company’s Equality and Diversity policy if when I move jobs because if I encounter a problem working there in this area, i’d need to refer to that. You could see if that helps you decide.
What’s their deal with this, from your knowledge of them? Are they ignorant, naïve, misogynistic, terrified not to get told to DIAF on social media, trying to push social boundaries, drastically misled about the reality of biological sex?
Does ‘style guide’ mean the rules for what you yourself would have to write if you took the job?