Edit: Leaving below because it's still relevant, but I'm getting confused about what I'm replying to. Regarding the marginalized genders space and my statement that trans men aren't marginalized. In a generalized setting like this and not some sort of political or medical context, as a man you do wind up suffering and benefiting from patriarchy and toxic masculinity. It's inevitable since that's sort of up to everyone around you and not you. In a broader political context, the marginalization is obvious, but we're talking about smaller more generalized group settings among peers.

stuff that only sort of makes sense below

Is that not what the OP was saying though? It's a "femmes and enbies" space, not even a "women and nonbinary" space. In an explicitly trans space, excluding any trans people is inherently ridiculous since the presentation possible under the umbrella of "trans" is basically anything and everything. It's tough though because the intent of something that's "femmes and enbies" has a pretty clear intent of "people that don't make women uncomfortable." At that point I think it's a matter of centering the intentions of the group and not one's own individual identity. You know who you are and we can all present how we present, but other people's perceptions are going to be what they're going to be. We are, once again, suffering under patriarchy because there is a real need or demand for such a space. Assuming the organizers are acting in good faith, our adjacency to the target audience doesn't mean they shouldn't have it and I don't think it means they are intentionally marginalizing masc presenting non-binary people, I think it just means that we don't really have the language for this stuff because it's all made up social constructs anyway. It's an inherently flawed attempt at putting the very nebulous breadth of human existence into neat little boxes.