Is this an essential qualification for being able to post here? And what exactly does it mean?

On /r/GC iirc the rule was simple and clear: content arguing against the right to abortion in any way would be removed.

I think you can probably still post and participate just fine, just don't post that specific disallowed content here. Or at least that was the rule. The rules may be different in the new forum. And of course they're different in other radfem spaces.

it's going to cut out a lot of women who are able and willing to fight against trans ideology.

The requirement to be a "radical feminist" arguably removed most women already, anyway. Most women are not radical feminists! on /r/GC it seemed like it was ok for women who were not radical feminists to post relevant stuff as long as they remained respectful that it was a radical feminist space. Like women posting asking for help with bad experiences they were having with men in their lives.

I've also seen posts elsewhere by conservative women who say they like to read GC but don't post because they know they're not radical feminists and that's fine, but they still appreciate the information.

I think it would be neat to just have a women's place where we could all talk to each other, differences and all.